diff --git a/upb/message/accessors.c b/upb/message/accessors.c
index 70a60a0..15531b9 100644
--- a/upb/message/accessors.c
+++ b/upb/message/accessors.c
@@ -15,6 +15,7 @@
 #include "upb/message/message.h"
 #include "upb/mini_table/field.h"
 #include "upb/mini_table/message.h"
+#include "upb/mini_table/sub.h"
 #include "upb/wire/encode.h"
 
 // Must be last.
@@ -22,11 +23,12 @@
 
 upb_MapInsertStatus upb_Message_InsertMapEntry(upb_Map* map,
                                                const upb_MiniTable* mini_table,
-                                               const upb_MiniTableField* field,
+                                               const upb_MiniTableField* f,
                                                upb_Message* map_entry_message,
                                                upb_Arena* arena) {
+  // TODO: use a variant of upb_MiniTable_GetSubMessageTable() here.
   const upb_MiniTable* map_entry_mini_table =
-      mini_table->subs[field->UPB_PRIVATE(submsg_index)].submsg;
+      upb_MiniTableSub_Message(mini_table->subs[f->UPB_PRIVATE(submsg_index)]);
   UPB_ASSERT(map_entry_mini_table);
   UPB_ASSERT(map_entry_mini_table->field_count == 2);
   const upb_MiniTableField* map_entry_key_field =
diff --git a/upb/message/accessors.h b/upb/message/accessors.h
index 703d506..d0b164b 100644
--- a/upb/message/accessors.h
+++ b/upb/message/accessors.h
@@ -28,10 +28,10 @@
 #include "upb/mini_table/extension.h"
 #include "upb/mini_table/field.h"
 #include "upb/mini_table/internal/field.h"
+#include "upb/mini_table/message.h"
+#include "upb/mini_table/sub.h"
 
 // Must be last.
-#include "upb/mini_table/internal/field.h"
-#include "upb/mini_table/message.h"
 #include "upb/port/def.inc"
 
 #ifdef __cplusplus
@@ -346,7 +346,8 @@
   UPB_ASSUME(UPB_PRIVATE(_upb_MiniTableField_GetRep)(field) ==
              UPB_SIZE(kUpb_FieldRep_4Byte, kUpb_FieldRep_8Byte));
   UPB_ASSUME(upb_MiniTableField_IsScalar(field));
-  UPB_ASSERT(mini_table->subs[field->UPB_PRIVATE(submsg_index)].submsg);
+  UPB_ASSERT(upb_MiniTableSub_Message(
+      mini_table->subs[field->UPB_PRIVATE(submsg_index)]));
   _upb_Message_SetNonExtensionField(msg, field, &sub_message);
 }
 
@@ -365,8 +366,8 @@
   UPB_ASSUME(upb_MiniTableField_CType(field) == kUpb_CType_Message);
   upb_Message* sub_message = *UPB_PTR_AT(msg, field->offset, upb_Message*);
   if (!sub_message) {
-    const upb_MiniTable* sub_mini_table =
-        mini_table->subs[field->UPB_PRIVATE(submsg_index)].submsg;
+    const upb_MiniTable* sub_mini_table = upb_MiniTableSub_Message(
+        mini_table->subs[field->UPB_PRIVATE(submsg_index)]);
     UPB_ASSERT(sub_mini_table);
     sub_message = _upb_Message_New(sub_mini_table, arena);
     *UPB_PTR_AT(msg, field->offset, upb_Message*) = sub_message;
diff --git a/upb/message/copy.c b/upb/message/copy.c
index 4be6573..8c0819b 100644
--- a/upb/message/copy.c
+++ b/upb/message/copy.c
@@ -29,6 +29,7 @@
 #include "upb/mini_table/internal/message.h"
 #include "upb/mini_table/internal/size_log2.h"
 #include "upb/mini_table/message.h"
+#include "upb/mini_table/sub.h"
 
 // Must be last.
 #include "upb/port/def.inc"
@@ -115,11 +116,12 @@
 
 static upb_Map* upb_Message_Map_DeepClone(const upb_Map* map,
                                           const upb_MiniTable* mini_table,
-                                          const upb_MiniTableField* field,
+                                          const upb_MiniTableField* f,
                                           upb_Message* clone,
                                           upb_Arena* arena) {
+  // TODO: use a variant of upb_MiniTable_GetSubMessageTable() here.
   const upb_MiniTable* map_entry_table =
-      mini_table->subs[field->UPB_PRIVATE(submsg_index)].submsg;
+      upb_MiniTableSub_Message(mini_table->subs[f->UPB_PRIVATE(submsg_index)]);
   UPB_ASSERT(map_entry_table);
 
   const upb_MiniTableField* key_field = &map_entry_table->fields[0];
@@ -131,7 +133,7 @@
   if (!cloned_map) {
     return NULL;
   }
-  _upb_Message_SetNonExtensionField(clone, field, &cloned_map);
+  _upb_Message_SetNonExtensionField(clone, f, &cloned_map);
   return cloned_map;
 }
 
@@ -267,9 +269,9 @@
     } else {
       upb_Array* msg_array = (upb_Array*)msg_ext->data.ptr;
       UPB_ASSERT(msg_array);
-      upb_Array* cloned_array =
-          upb_Array_DeepClone(msg_array, upb_MiniTableField_CType(field),
-                              msg_ext->ext->UPB_PRIVATE(sub).submsg, arena);
+      upb_Array* cloned_array = upb_Array_DeepClone(
+          msg_array, upb_MiniTableField_CType(field),
+          upb_MiniTableExtension_GetSubMessage(msg_ext->ext), arena);
       if (!cloned_array) {
         return NULL;
       }
diff --git a/upb/message/promote.c b/upb/message/promote.c
index acd3192..bffc9a0 100644
--- a/upb/message/promote.c
+++ b/upb/message/promote.c
@@ -26,6 +26,7 @@
 #include "upb/mini_table/field.h"
 #include "upb/mini_table/internal/field.h"
 #include "upb/mini_table/message.h"
+#include "upb/mini_table/sub.h"
 #include "upb/wire/decode.h"
 #include "upb/wire/eps_copy_input_stream.h"
 #include "upb/wire/internal/constants.h"
@@ -324,8 +325,9 @@
 upb_UnknownToMessage_Status upb_MiniTable_PromoteUnknownToMap(
     upb_Message* msg, const upb_MiniTable* mini_table,
     const upb_MiniTableField* field, int decode_options, upb_Arena* arena) {
-  const upb_MiniTable* map_entry_mini_table =
-      mini_table->subs[field->UPB_PRIVATE(submsg_index)].submsg;
+  // TODO: use a variant of upb_MiniTable_GetSubMessageTable() here.
+  const upb_MiniTable* map_entry_mini_table = upb_MiniTableSub_Message(
+      mini_table->subs[field->UPB_PRIVATE(submsg_index)]);
   UPB_ASSERT(map_entry_mini_table);
   UPB_ASSERT(map_entry_mini_table);
   UPB_ASSERT(map_entry_mini_table->field_count == 2);
diff --git a/upb/message/tagged_ptr.h b/upb/message/tagged_ptr.h
index 2596cd7..9004c77 100644
--- a/upb/message/tagged_ptr.h
+++ b/upb/message/tagged_ptr.h
@@ -5,8 +5,8 @@
 // license that can be found in the LICENSE file or at
 // https://developers.google.com/open-source/licenses/bsd
 
-#ifndef UPB_MINI_TABLE_TYPES_H_
-#define UPB_MINI_TABLE_TYPES_H_
+#ifndef UPB_MINI_TABLE_TAGGED_PTR_H_
+#define UPB_MINI_TABLE_TAGGED_PTR_H_
 
 #include <stdint.h>
 
@@ -15,10 +15,6 @@
 // Must be last.
 #include "upb/port/def.inc"
 
-#ifdef __cplusplus
-extern "C" {
-#endif
-
 // When a upb_Message* is stored in a message, array, or map, it is stored in a
 // tagged form.  If the tag bit is set, the referenced upb_Message is of type
 // _kUpb_MiniTable_Empty (a sentinel message type with no fields) instead of
@@ -27,8 +23,13 @@
 //
 // See the documentation for kUpb_DecodeOption_ExperimentalAllowUnlinked for
 // more information.
+
 typedef uintptr_t upb_TaggedMessagePtr;
 
+#ifdef __cplusplus
+extern "C" {
+#endif
+
 // Internal-only because empty messages cannot be created by the user.
 UPB_INLINE upb_TaggedMessagePtr _upb_TaggedMessagePtr_Pack(upb_Message* ptr,
                                                            bool empty) {
@@ -66,4 +67,4 @@
 
 #include "upb/port/undef.inc"
 
-#endif /* UPB_MINI_TABLE_TYPES_H_ */
+#endif /* UPB_MINI_TABLE_TAGGED_PTR_H_ */
diff --git a/upb/mini_descriptor/decode.c b/upb/mini_descriptor/decode.c
index 15db665..b104bc1 100644
--- a/upb/mini_descriptor/decode.c
+++ b/upb/mini_descriptor/decode.c
@@ -394,7 +394,7 @@
   upb_MdDecoder_CheckOutOfMemory(&d->base, subs);
   uint32_t i = 0;
   for (; i < sub_counts.submsg_count; i++) {
-    subs[i].submsg = &_kUpb_MiniTable_Empty;
+    subs[i].UPB_PRIVATE(submsg) = &_kUpb_MiniTable_Empty;
   }
   if (sub_counts.subenum_count) {
     upb_MiniTableField* f = d->fields;
@@ -405,7 +405,7 @@
       }
     }
     for (; i < sub_counts.submsg_count + sub_counts.subenum_count; i++) {
-      subs[i].subenum = NULL;
+      subs[i].UPB_PRIVATE(subenum) = NULL;
     }
   }
   d->table->subs = subs;
diff --git a/upb/mini_descriptor/decode.h b/upb/mini_descriptor/decode.h
index ec7c12e..dedf24f 100644
--- a/upb/mini_descriptor/decode.h
+++ b/upb/mini_descriptor/decode.h
@@ -76,8 +76,7 @@
 UPB_API_INLINE upb_MiniTableExtension* upb_MiniTableExtension_Build(
     const char* data, size_t len, const upb_MiniTable* extendee,
     upb_Arena* arena, upb_Status* status) {
-  upb_MiniTableSub sub;
-  sub.submsg = NULL;
+  upb_MiniTableSub sub = upb_MiniTableSub_FromMessage(NULL);
   return _upb_MiniTableExtension_Build(
       data, len, extendee, sub, kUpb_MiniTablePlatform_Native, arena, status);
 }
@@ -85,8 +84,7 @@
 UPB_API_INLINE upb_MiniTableExtension* upb_MiniTableExtension_BuildMessage(
     const char* data, size_t len, const upb_MiniTable* extendee,
     upb_MiniTable* submsg, upb_Arena* arena, upb_Status* status) {
-  upb_MiniTableSub sub;
-  sub.submsg = submsg;
+  upb_MiniTableSub sub = upb_MiniTableSub_FromMessage(submsg);
   return _upb_MiniTableExtension_Build(
       data, len, extendee, sub, kUpb_MiniTablePlatform_Native, arena, status);
 }
@@ -94,8 +92,7 @@
 UPB_API_INLINE upb_MiniTableExtension* upb_MiniTableExtension_BuildEnum(
     const char* data, size_t len, const upb_MiniTable* extendee,
     upb_MiniTableEnum* subenum, upb_Arena* arena, upb_Status* status) {
-  upb_MiniTableSub sub;
-  sub.subenum = subenum;
+  upb_MiniTableSub sub = upb_MiniTableSub_FromEnum(subenum);
   return _upb_MiniTableExtension_Build(
       data, len, extendee, sub, kUpb_MiniTablePlatform_Native, arena, status);
 }
diff --git a/upb/mini_descriptor/internal/encode_test.cc b/upb/mini_descriptor/internal/encode_test.cc
index 5da2443..7d1663d 100644
--- a/upb/mini_descriptor/internal/encode_test.cc
+++ b/upb/mini_descriptor/internal/encode_test.cc
@@ -28,6 +28,7 @@
 #include "upb/mini_table/internal/field.h"
 #include "upb/mini_table/internal/message.h"
 #include "upb/mini_table/message.h"
+#include "upb/mini_table/sub.h"
 
 // begin:google_only
 // #include "testing/fuzzing/fuzztest.h"
@@ -240,8 +241,8 @@
       e.data().data(), e.data().size(), GetParam(), arena.ptr(), status.ptr());
   ASSERT_NE(nullptr, table);
   EXPECT_EQ(table->field_count, 2);
-  EXPECT_EQ(table->subs[0].submsg, &_kUpb_MiniTable_Empty);
-  EXPECT_EQ(table->subs[1].submsg, &_kUpb_MiniTable_Empty);
+  EXPECT_EQ(upb_MiniTableSub_Message(table->subs[0]), &_kUpb_MiniTable_Empty);
+  EXPECT_EQ(upb_MiniTableSub_Message(table->subs[1]), &_kUpb_MiniTable_Empty);
 }
 
 TEST(MiniTableEnumTest, PositiveAndNegative) {
diff --git a/upb/mini_descriptor/link.c b/upb/mini_descriptor/link.c
index 39da601..4fc6344 100644
--- a/upb/mini_descriptor/link.c
+++ b/upb/mini_descriptor/link.c
@@ -7,6 +7,17 @@
 
 #include "upb/mini_descriptor/link.h"
 
+#include <stddef.h>
+#include <stdint.h>
+
+#include "upb/base/descriptor_constants.h"
+#include "upb/mini_table/enum.h"
+#include "upb/mini_table/field.h"
+#include "upb/mini_table/internal/field.h"
+#include "upb/mini_table/internal/message.h"
+#include "upb/mini_table/message.h"
+#include "upb/mini_table/sub.h"
+
 // Must be last.
 #include "upb/port/def.inc"
 
@@ -43,7 +54,7 @@
   // TODO: Add this assert back once YouTube is updated to not call
   // this function repeatedly.
   // UPB_ASSERT(table_sub->submsg == &_kUpb_MiniTable_Empty);
-  table_sub->submsg = sub;
+  *table_sub = upb_MiniTableSub_FromMessage(sub);
   return true;
 }
 
@@ -56,7 +67,7 @@
 
   upb_MiniTableSub* table_sub =
       (void*)&table->subs[field->UPB_PRIVATE(submsg_index)];
-  table_sub->subenum = sub;
+  *table_sub = upb_MiniTableSub_FromEnum(sub);
   return true;
 }
 
diff --git a/upb/mini_table/internal/extension.h b/upb/mini_table/internal/extension.h
index b059324..7625944 100644
--- a/upb/mini_table/internal/extension.h
+++ b/upb/mini_table/internal/extension.h
@@ -41,12 +41,12 @@
 UPB_INLINE const struct upb_MiniTable* UPB_PRIVATE(
     _upb_MiniTableExtension_GetSubMessage)(
     const struct upb_MiniTableExtension* e) {
-  return e->UPB_PRIVATE(sub).submsg;
+  return e->UPB_PRIVATE(sub).UPB_PRIVATE(submsg);
 }
 
 UPB_INLINE void UPB_PRIVATE(_upb_MiniTableExtension_SetSubMessage)(
     struct upb_MiniTableExtension* e, const struct upb_MiniTable* m) {
-  e->UPB_PRIVATE(sub).submsg = m;
+  e->UPB_PRIVATE(sub).UPB_PRIVATE(submsg) = m;
 }
 
 #ifdef __cplusplus
diff --git a/upb/mini_table/internal/sub.h b/upb/mini_table/internal/sub.h
index fe236db..99e35bd 100644
--- a/upb/mini_table/internal/sub.h
+++ b/upb/mini_table/internal/sub.h
@@ -12,10 +12,42 @@
 #include "upb/port/def.inc"
 
 union upb_MiniTableSub {
-  const struct upb_MiniTable* submsg;
-  const struct upb_MiniTableEnum* subenum;
+  const struct upb_MiniTable* UPB_PRIVATE(submsg);
+  const struct upb_MiniTableEnum* UPB_PRIVATE(subenum);
 };
 
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+UPB_INLINE union upb_MiniTableSub UPB_PRIVATE(_upb_MiniTableSub_FromEnum)(
+    const struct upb_MiniTableEnum* subenum) {
+  union upb_MiniTableSub out;
+  out.UPB_PRIVATE(subenum) = subenum;
+  return out;
+}
+
+UPB_INLINE union upb_MiniTableSub UPB_PRIVATE(_upb_MiniTableSub_FromMessage)(
+    const struct upb_MiniTable* submsg) {
+  union upb_MiniTableSub out;
+  out.UPB_PRIVATE(submsg) = submsg;
+  return out;
+}
+
+UPB_INLINE const struct upb_MiniTableEnum* UPB_PRIVATE(_upb_MiniTableSub_Enum)(
+    const union upb_MiniTableSub sub) {
+  return sub.UPB_PRIVATE(subenum);
+}
+
+UPB_INLINE const struct upb_MiniTable* UPB_PRIVATE(_upb_MiniTableSub_Message)(
+    const union upb_MiniTableSub sub) {
+  return sub.UPB_PRIVATE(submsg);
+}
+
+#ifdef __cplusplus
+} /* extern "C" */
+#endif
+
 #include "upb/port/undef.inc"
 
 #endif /* UPB_MINI_TABLE_INTERNAL_SUB_H_ */
diff --git a/upb/mini_table/message.h b/upb/mini_table/message.h
index 332338c..3375570 100644
--- a/upb/mini_table/message.h
+++ b/upb/mini_table/message.h
@@ -11,7 +11,7 @@
 #include "upb/mini_table/enum.h"
 #include "upb/mini_table/field.h"
 #include "upb/mini_table/internal/message.h"
-#include "upb/mini_table/internal/sub.h"
+#include "upb/mini_table/sub.h"
 
 // Must be last.
 #include "upb/port/def.inc"
@@ -35,8 +35,8 @@
 UPB_API_INLINE const upb_MiniTable* upb_MiniTable_GetSubMessageTable(
     const upb_MiniTable* mini_table, const upb_MiniTableField* field) {
   UPB_ASSERT(upb_MiniTableField_CType(field) == kUpb_CType_Message);
-  const upb_MiniTable* ret =
-      mini_table->subs[field->UPB_PRIVATE(submsg_index)].submsg;
+  const upb_MiniTable* ret = upb_MiniTableSub_Message(
+      mini_table->subs[field->UPB_PRIVATE(submsg_index)]);
   UPB_ASSUME(ret);
   return ret == &_kUpb_MiniTable_Empty ? NULL : ret;
 }
@@ -44,9 +44,9 @@
 // Returns the MiniTableEnum for this enum field.  If the field is unlinked,
 // returns NULL.
 UPB_API_INLINE const upb_MiniTableEnum* upb_MiniTable_GetSubEnumTable(
-    const upb_MiniTable* mini_table, const upb_MiniTableField* field) {
-  UPB_ASSERT(upb_MiniTableField_CType(field) == kUpb_CType_Enum);
-  return mini_table->subs[field->UPB_PRIVATE(submsg_index)].subenum;
+    const upb_MiniTable* mini_table, const upb_MiniTableField* f) {
+  UPB_ASSERT(upb_MiniTableField_CType(f) == kUpb_CType_Enum);
+  return upb_MiniTableSub_Enum(mini_table->subs[f->UPB_PRIVATE(submsg_index)]);
 }
 
 // Returns true if this MiniTable field is linked to a MiniTable for the
diff --git a/upb/mini_table/sub.h b/upb/mini_table/sub.h
index 1c5d67e..cd2253a 100644
--- a/upb/mini_table/sub.h
+++ b/upb/mini_table/sub.h
@@ -10,6 +10,43 @@
 
 #include "upb/mini_table/internal/sub.h"
 
+// Must be last.
+#include "upb/port/def.inc"
+
 typedef union upb_MiniTableSub upb_MiniTableSub;
 
-#endif /* UPB_MINI_TABLE_INTERNAL_SUB_H_ */
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+// Constructors
+
+UPB_API_INLINE upb_MiniTableSub
+upb_MiniTableSub_FromEnum(const struct upb_MiniTableEnum* subenum) {
+  return UPB_PRIVATE(_upb_MiniTableSub_FromEnum)(subenum);
+}
+
+UPB_API_INLINE upb_MiniTableSub
+upb_MiniTableSub_FromMessage(const struct upb_MiniTable* submsg) {
+  return UPB_PRIVATE(_upb_MiniTableSub_FromMessage)(submsg);
+}
+
+// Getters
+
+UPB_API_INLINE const struct upb_MiniTableEnum* upb_MiniTableSub_Enum(
+    upb_MiniTableSub sub) {
+  return UPB_PRIVATE(_upb_MiniTableSub_Enum)(sub);
+}
+
+UPB_API_INLINE const struct upb_MiniTable* upb_MiniTableSub_Message(
+    upb_MiniTableSub sub) {
+  return UPB_PRIVATE(_upb_MiniTableSub_Message)(sub);
+}
+
+#ifdef __cplusplus
+} /* extern "C" */
+#endif
+
+#include "upb/port/undef.inc"
+
+#endif /* UPB_MINI_TABLE_SUB_H_ */
diff --git a/upb/reflection/field_def.c b/upb/reflection/field_def.c
index a6d287c..bf29ff0 100644
--- a/upb/reflection/field_def.c
+++ b/upb/reflection/field_def.c
@@ -22,6 +22,7 @@
 #include "upb/mini_descriptor/decode.h"
 #include "upb/mini_descriptor/internal/encode.h"
 #include "upb/mini_descriptor/internal/modifiers.h"
+#include "upb/mini_table/enum.h"
 #include "upb/mini_table/extension.h"
 #include "upb/mini_table/field.h"
 #include "upb/mini_table/message.h"
@@ -934,9 +935,11 @@
     upb_MiniTableExtension* mut_ext = (upb_MiniTableExtension*)ext;
     upb_MiniTableSub sub = {NULL};
     if (upb_FieldDef_IsSubMessage(f)) {
-      sub.submsg = upb_MessageDef_MiniTable(f->sub.msgdef);
+      const upb_MiniTable* submsg = upb_MessageDef_MiniTable(f->sub.msgdef);
+      sub = upb_MiniTableSub_FromMessage(submsg);
     } else if (_upb_FieldDef_IsClosedEnum(f)) {
-      sub.subenum = _upb_EnumDef_MiniTable(f->sub.enumdef);
+      const upb_MiniTableEnum* subenum = _upb_EnumDef_MiniTable(f->sub.enumdef);
+      sub = upb_MiniTableSub_FromEnum(subenum);
     }
     bool ok2 = upb_MiniTableExtension_Init(desc.data, desc.size, mut_ext,
                                            upb_MessageDef_MiniTable(f->msgdef),
diff --git a/upb/test/fuzz_util.cc b/upb/test/fuzz_util.cc
index 299ab24..613e63c 100644
--- a/upb/test/fuzz_util.cc
+++ b/upb/test/fuzz_util.cc
@@ -101,12 +101,12 @@
   if (upb_MiniTableField_CType(field) == kUpb_CType_Message) {
     auto mt = NextMiniTable();
     if (!mt) field->UPB_PRIVATE(descriptortype) = kUpb_FieldType_Int32;
-    ext->UPB_PRIVATE(sub).submsg = mt;
+    ext->UPB_PRIVATE(sub) = upb_MiniTableSub_FromMessage(mt);
   }
   if (upb_MiniTableField_IsClosedEnum(field)) {
     auto et = NextEnumTable();
     if (!et) field->UPB_PRIVATE(descriptortype) = kUpb_FieldType_Int32;
-    ext->UPB_PRIVATE(sub).subenum = et;
+    ext->UPB_PRIVATE(sub) = upb_MiniTableSub_FromEnum(et);
   }
   return true;
 }
diff --git a/upb/wire/decode.c b/upb/wire/decode.c
index 113bf55..0e1a6fc 100644
--- a/upb/wire/decode.c
+++ b/upb/wire/decode.c
@@ -87,6 +87,25 @@
   uint32_t size;
 } wireval;
 
+// Ideally these two functions should take the owning MiniTable pointer as a
+// first argument, then we could just put them in mini_table/message.h as nice
+// clean getters. But we don't have that so instead we gotta write these
+// Frankenfunctions that take an array of subtables.
+
+// Returns the MiniTable corresponding to a given MiniTableField
+// from an array of MiniTableSubs.
+static const upb_MiniTable* _upb_MiniTableSubs_MessageByField(
+    const upb_MiniTableSub* subs, const upb_MiniTableField* field) {
+  return upb_MiniTableSub_Message(subs[field->UPB_PRIVATE(submsg_index)]);
+}
+
+// Returns the MiniTableEnum corresponding to a given MiniTableField
+// from an array of MiniTableSub.
+static const upb_MiniTableEnum* _upb_MiniTableSubs_EnumByField(
+    const upb_MiniTableSub* subs, const upb_MiniTableField* field) {
+  return upb_MiniTableSub_Enum(subs[field->UPB_PRIVATE(submsg_index)]);
+}
+
 static const char* _upb_Decoder_DecodeMessage(upb_Decoder* d, const char* ptr,
                                               upb_Message* msg,
                                               const upb_MiniTable* layout);
@@ -223,7 +242,7 @@
                                                const upb_MiniTableSub* subs,
                                                const upb_MiniTableField* field,
                                                upb_TaggedMessagePtr* target) {
-  const upb_MiniTable* subl = subs[field->UPB_PRIVATE(submsg_index)].submsg;
+  const upb_MiniTable* subl = _upb_MiniTableSubs_MessageByField(subs, field);
   UPB_ASSERT(subl);
   upb_Message* msg = _upb_Message_New(subl, &d->arena);
   if (!msg) _upb_Decoder_ErrorJmp(d, kUpb_DecodeStatus_OutOfMemory);
@@ -247,7 +266,7 @@
     upb_Decoder* d, const upb_MiniTableSub* subs,
     const upb_MiniTableField* field, upb_TaggedMessagePtr* target) {
   upb_TaggedMessagePtr tagged = *target;
-  const upb_MiniTable* subl = subs[field->UPB_PRIVATE(submsg_index)].submsg;
+  const upb_MiniTable* subl = _upb_MiniTableSubs_MessageByField(subs, field);
   UPB_ASSERT(subl);
   if (!upb_TaggedMessagePtr_IsEmpty(tagged) || subl == &_kUpb_MiniTable_Empty) {
     return _upb_TaggedMessagePtr_GetMessage(tagged);
@@ -298,7 +317,7 @@
     upb_Decoder* d, const char* ptr, upb_Message* submsg,
     const upb_MiniTableSub* subs, const upb_MiniTableField* field, int size) {
   int saved_delta = upb_EpsCopyInputStream_PushLimit(&d->input, ptr, size);
-  const upb_MiniTable* subl = subs[field->UPB_PRIVATE(submsg_index)].submsg;
+  const upb_MiniTable* subl = _upb_MiniTableSubs_MessageByField(subs, field);
   UPB_ASSERT(subl);
   ptr = _upb_Decoder_RecurseSubMessage(d, ptr, submsg, subl, DECODE_NOGROUP);
   upb_EpsCopyInputStream_PopLimit(&d->input, ptr, saved_delta);
@@ -329,7 +348,7 @@
 static const char* _upb_Decoder_DecodeKnownGroup(
     upb_Decoder* d, const char* ptr, upb_Message* submsg,
     const upb_MiniTableSub* subs, const upb_MiniTableField* field) {
-  const upb_MiniTable* subl = subs[field->UPB_PRIVATE(submsg_index)].submsg;
+  const upb_MiniTable* subl = _upb_MiniTableSubs_MessageByField(subs, field);
   UPB_ASSERT(subl);
   return _upb_Decoder_DecodeGroup(d, ptr, submsg, subl, field->number);
 }
@@ -382,7 +401,7 @@
                                                 const upb_MiniTableSub* subs,
                                                 const upb_MiniTableField* field,
                                                 wireval* val) {
-  const upb_MiniTableEnum* e = subs[field->UPB_PRIVATE(submsg_index)].subenum;
+  const upb_MiniTableEnum* e = _upb_MiniTableSubs_EnumByField(subs, field);
   if (!_upb_Decoder_CheckEnum(d, ptr, msg, e, field, val)) return ptr;
   void* mem = UPB_PTR_AT(_upb_array_ptr(arr), arr->size * 4, void);
   arr->size++;
@@ -453,7 +472,7 @@
     upb_Decoder* d, const char* ptr, upb_Message* msg, upb_Array* arr,
     const upb_MiniTableSub* subs, const upb_MiniTableField* field,
     wireval* val) {
-  const upb_MiniTableEnum* e = subs[field->UPB_PRIVATE(submsg_index)].subenum;
+  const upb_MiniTableEnum* e = _upb_MiniTableSubs_EnumByField(subs, field);
   int saved_limit = upb_EpsCopyInputStream_PushLimit(&d->input, ptr, val->size);
   char* out = UPB_PTR_AT(_upb_array_ptr(arr), arr->size * 4, void);
   while (!_upb_Decoder_IsDone(d, &ptr)) {
@@ -593,7 +612,7 @@
   upb_Map* map = *map_p;
   upb_MapEntry ent;
   UPB_ASSERT(upb_MiniTableField_Type(field) == kUpb_FieldType_Message);
-  const upb_MiniTable* entry = subs[field->UPB_PRIVATE(submsg_index)].submsg;
+  const upb_MiniTable* entry = _upb_MiniTableSubs_MessageByField(subs, field);
 
   UPB_ASSERT(entry);
   UPB_ASSERT(entry->field_count == 2);
@@ -653,7 +672,7 @@
 
   if (UPB_UNLIKELY(op == kUpb_DecodeOp_Enum) &&
       !_upb_Decoder_CheckEnum(d, ptr, msg,
-                              subs[field->UPB_PRIVATE(submsg_index)].subenum,
+                              _upb_MiniTableSubs_EnumByField(subs, field),
                               field, val)) {
     return ptr;
   }
@@ -971,9 +990,10 @@
                                        int* op) {
   // If sub-message is not linked, treat as unknown.
   if (field->mode & kUpb_LabelFlags_IsExtension) return;
-  const upb_MiniTableSub* sub = &mt->subs[field->UPB_PRIVATE(submsg_index)];
+  const upb_MiniTable* mt_sub =
+      _upb_MiniTableSubs_MessageByField(mt->subs, field);
   if ((d->options & kUpb_DecodeOption_ExperimentalAllowUnlinked) ||
-      sub->submsg != &_kUpb_MiniTable_Empty) {
+      mt_sub != &_kUpb_MiniTable_Empty) {
     return;
   }
 #ifndef NDEBUG
diff --git a/upb/wire/decode_fast.c b/upb/wire/decode_fast.c
index 5a412ef..a77aea3 100644
--- a/upb/wire/decode_fast.c
+++ b/upb/wire/decode_fast.c
@@ -20,6 +20,7 @@
 #include "upb/message/array.h"
 #include "upb/message/internal/array.h"
 #include "upb/message/internal/types.h"
+#include "upb/mini_table/sub.h"
 #include "upb/wire/internal/decode.h"
 
 // Must be last.
@@ -914,7 +915,8 @@
   upb_Message** dst;                                                      \
   uint32_t submsg_idx = (data >> 16) & 0xff;                              \
   const upb_MiniTable* tablep = decode_totablep(table);                   \
-  const upb_MiniTable* subtablep = tablep->subs[submsg_idx].submsg;       \
+  const upb_MiniTable* subtablep =                                        \
+      upb_MiniTableSub_Message(tablep->subs[submsg_idx]);                 \
   fastdecode_submsgdata submsg = {decode_totable(subtablep)};             \
   fastdecode_arr farr;                                                    \
                                                                           \
diff --git a/upb/wire/encode.c b/upb/wire/encode.c
index ca2b465..30cef79 100644
--- a/upb/wire/encode.c
+++ b/upb/wire/encode.c
@@ -271,7 +271,8 @@
     case kUpb_FieldType_Group: {
       size_t size;
       upb_TaggedMessagePtr submsg = *(upb_TaggedMessagePtr*)field_mem;
-      const upb_MiniTable* subm = subs[f->UPB_PRIVATE(submsg_index)].submsg;
+      const upb_MiniTable* subm =
+          upb_MiniTableSub_Message(subs[f->UPB_PRIVATE(submsg_index)]);
       if (submsg == 0) {
         return;
       }
@@ -285,7 +286,8 @@
     case kUpb_FieldType_Message: {
       size_t size;
       upb_TaggedMessagePtr submsg = *(upb_TaggedMessagePtr*)field_mem;
-      const upb_MiniTable* subm = subs[f->UPB_PRIVATE(submsg_index)].submsg;
+      const upb_MiniTable* subm =
+          upb_MiniTableSub_Message(subs[f->UPB_PRIVATE(submsg_index)]);
       if (submsg == 0) {
         return;
       }
@@ -374,7 +376,8 @@
     case kUpb_FieldType_Group: {
       const upb_TaggedMessagePtr* start = _upb_array_constptr(arr);
       const upb_TaggedMessagePtr* ptr = start + arr->size;
-      const upb_MiniTable* subm = subs[f->UPB_PRIVATE(submsg_index)].submsg;
+      const upb_MiniTable* subm =
+          upb_MiniTableSub_Message(subs[f->UPB_PRIVATE(submsg_index)]);
       if (--e->depth == 0) encode_err(e, kUpb_EncodeStatus_MaxDepthExceeded);
       do {
         size_t size;
@@ -389,7 +392,8 @@
     case kUpb_FieldType_Message: {
       const upb_TaggedMessagePtr* start = _upb_array_constptr(arr);
       const upb_TaggedMessagePtr* ptr = start + arr->size;
-      const upb_MiniTable* subm = subs[f->UPB_PRIVATE(submsg_index)].submsg;
+      const upb_MiniTable* subm =
+          upb_MiniTableSub_Message(subs[f->UPB_PRIVATE(submsg_index)]);
       if (--e->depth == 0) encode_err(e, kUpb_EncodeStatus_MaxDepthExceeded);
       do {
         size_t size;
@@ -428,7 +432,8 @@
                        const upb_MiniTableSub* subs,
                        const upb_MiniTableField* f) {
   const upb_Map* map = *UPB_PTR_AT(msg, f->offset, const upb_Map*);
-  const upb_MiniTable* layout = subs[f->UPB_PRIVATE(submsg_index)].submsg;
+  const upb_MiniTable* layout =
+      upb_MiniTableSub_Message(subs[f->UPB_PRIVATE(submsg_index)]);
   UPB_ASSERT(layout->field_count == 2);
 
   if (map == NULL) return;
diff --git a/upb_generator/protoc-gen-upb_minitable.cc b/upb_generator/protoc-gen-upb_minitable.cc
index 79b59eb..2f58330 100644
--- a/upb_generator/protoc-gen-upb_minitable.cc
+++ b/upb_generator/protoc-gen-upb_minitable.cc
@@ -385,16 +385,18 @@
 
 std::string GetSub(upb::FieldDefPtr field) {
   if (auto message_def = field.message_type()) {
-    return absl::Substitute("{.submsg = &$0}", MessageInitName(message_def));
+    return absl::Substitute("{.UPB_PRIVATE(submsg) = &$0}",
+                            MessageInitName(message_def));
   }
 
   if (auto enum_def = field.enum_subdef()) {
     if (enum_def.is_closed()) {
-      return absl::Substitute("{.subenum = &$0}", EnumInit(enum_def));
+      return absl::Substitute("{.UPB_PRIVATE(subenum) = &$0}",
+                              EnumInit(enum_def));
     }
   }
 
-  return std::string("{.submsg = NULL}");
+  return std::string("{.UPB_PRIVATE(submsg) = NULL}");
 }
 
 // Writes a single message into a .upb.c source file.