diff --git a/bazel/build_defs.bzl b/bazel/build_defs.bzl
index e5c270d..ba7a037 100644
--- a/bazel/build_defs.bzl
+++ b/bazel/build_defs.bzl
@@ -41,8 +41,6 @@
 ])
 _DEFAULT_COPTS.extend([
     "-std=c99",
-    "-pedantic",
-    "-Werror=pedantic",
     "-Wall",
     "-Wstrict-prototypes",
     # GCC (at least) emits spurious warnings for this that cannot be fixed
diff --git a/upb/decode.c b/upb/decode.c
index 8ba5c21..b3bcc0a 100644
--- a/upb/decode.c
+++ b/upb/decode.c
@@ -31,6 +31,7 @@
 
 #include "upb/internal/array.h"
 #include "upb/internal/decode.h"
+#include "upb/msg_internal.h"
 #include "upb/upb.h"
 
 // Must be last.
@@ -421,11 +422,7 @@
                                        const upb_MiniTable_Enum* e,
                                        const upb_MiniTable_Field* field,
                                        uint32_t v) {
-  // OPT: binary search long lists?
-  int n = e->value_count;
-  for (int i = 0; i < n; i++) {
-    if ((uint32_t)e->values[i] == v) return true;
-  }
+  if (_upb_MiniTable_CheckEnumValueSlow(e, v)) return true;
 
   // Unrecognized enum goes into unknown fields.
   // For packed fields the tag could be arbitrarily far in the past, so we
@@ -445,8 +442,8 @@
                                    wireval* val) {
   uint32_t v = val->uint32_val;
 
-  if (UPB_LIKELY(v < 64) && UPB_LIKELY(((1ULL << v) & e->mask))) return true;
-
+  _kUpb_FastEnumCheck_Status status = _upb_MiniTable_CheckEnumValueFast(e, v);
+  if (UPB_LIKELY(status == _kUpb_FastEnumCheck_ValueIsInEnum)) return true;
   return _upb_Decoder_CheckEnumSlow(d, ptr, msg, e, field, v);
 }
 
diff --git a/upb/def.c b/upb/def.c
index a7144be..002faf5 100644
--- a/upb/def.c
+++ b/upb/def.c
@@ -2644,8 +2644,6 @@
     if (ctx->layout) {
       UPB_ASSERT(ctx->enum_count < ctx->layout->enum_count);
       e->layout = ctx->layout->enums[ctx->enum_count++];
-      UPB_ASSERT(upb_inttable_count(&e->iton) ==
-                 e->layout->value_count + count_bits_debug(e->layout->mask));
     } else {
       e->layout = create_enumlayout(ctx, e);
     }
diff --git a/upb/mini_table.c b/upb/mini_table.c
index 3d13780..0f0592e 100644
--- a/upb/mini_table.c
+++ b/upb/mini_table.c
@@ -30,6 +30,7 @@
 #include <inttypes.h>
 #include <setjmp.h>
 
+#include "upb/arena.h"
 #include "upb/msg_internal.h"
 #include "upb/upb.h"
 
@@ -387,6 +388,13 @@
   upb_LayoutItemVector vec;
   upb_Arena* arena;
   upb_Status* status;
+
+  // When building enums.
+  upb_MiniTable_Enum* enum_table;
+  uint32_t enum_value_count;
+  uint32_t enum_data_count;
+  uint32_t enum_data_capacity;
+
   jmp_buf err;
 } upb_MtDecoder;
 
@@ -1034,41 +1042,67 @@
   return ret;
 }
 
-static bool upb_MiniTable_BuildEnumValue(upb_MtDecoder* d,
-                                         upb_MiniTable_Enum* table,
-                                         uint32_t val, upb_Arena* arena) {
-  if (val < 64) {
-    table->mask |= 1ULL << val;
-    return true;
-  }
+static size_t upb_MiniTable_EnumSize(size_t count) {
+  return sizeof(upb_MiniTable_Enum) + count * sizeof(uint32_t);
+}
 
-  int32_t* values = (void*)table->values;
-  values = upb_Arena_Realloc(arena, values, table->value_count * 4,
-                             (table->value_count + 1) * 4);
-  upb_MtDecoder_CheckOutOfMemory(d, values);
-  values[table->value_count++] = (int32_t)val;
-  table->values = values;
-  return true;
+static upb_MiniTable_Enum* _upb_MiniTable_AddEnumDataMember(upb_MtDecoder* d,
+                                                            uint32_t val) {
+  if (d->enum_data_count == d->enum_data_capacity) {
+    size_t old_sz = upb_MiniTable_EnumSize(d->enum_data_capacity);
+    d->enum_data_capacity = UPB_MAX(2, d->enum_data_capacity * 2);
+    size_t new_sz = upb_MiniTable_EnumSize(d->enum_data_capacity);
+    d->enum_table = upb_Arena_Realloc(d->arena, d->enum_table, old_sz, new_sz);
+    upb_MtDecoder_CheckOutOfMemory(d, d->enum_table);
+  }
+  d->enum_table->data[d->enum_data_count++] = val;
+  return d->enum_table;
+}
+
+static void upb_MiniTable_BuildEnumValue(upb_MtDecoder* d, uint32_t val) {
+  upb_MiniTable_Enum* table = d->enum_table;
+  d->enum_value_count++;
+  if (table->value_count || (val > 512 && d->enum_value_count < val / 32)) {
+    if (table->value_count == 0) {
+      assert(d->enum_data_count == table->mask_limit / 32);
+    }
+    table = _upb_MiniTable_AddEnumDataMember(d, val);
+    table->value_count++;
+  } else {
+    uint32_t new_mask_limit = ((val / 32) + 1) * 32;
+    while (table->mask_limit < new_mask_limit) {
+      table = _upb_MiniTable_AddEnumDataMember(d, 0);
+      table->mask_limit += 32;
+    }
+    table->data[val / 32] |= 1ULL << (val % 32);
+  }
 }
 
 upb_MiniTable_Enum* upb_MiniTable_BuildEnum(const char* data, size_t len,
                                             upb_Arena* arena,
                                             upb_Status* status) {
   upb_MtDecoder d = {
+      .enum_table = upb_Arena_Malloc(arena, upb_MiniTable_EnumSize(2)),
+      .enum_value_count = 0,
+      .enum_data_count = 0,
+      .enum_data_capacity = 1,
       .status = status,
       .end = UPB_PTRADD(data, len),
+      .arena = arena,
   };
 
   if (UPB_SETJMP(d.err)) {
     return NULL;
   }
 
-  upb_MiniTable_Enum* table = upb_Arena_Malloc(arena, sizeof(*table));
-  upb_MtDecoder_CheckOutOfMemory(&d, table);
+  upb_MtDecoder_CheckOutOfMemory(&d, d.enum_table);
 
-  table->mask = 0;
-  table->value_count = 0;
-  table->values = NULL;
+  // Guarantee at least 64 bits of mask without checking mask size.
+  d.enum_table->mask_limit = 64;
+  d.enum_table = _upb_MiniTable_AddEnumDataMember(&d, 0);
+  d.enum_table = _upb_MiniTable_AddEnumDataMember(&d, 0);
+
+  d.enum_table->value_count = 0;
 
   const char* ptr = data;
   uint32_t base = 0;
@@ -1078,11 +1112,7 @@
     if (ch <= kUpb_EncodedValue_MaxEnumMask) {
       uint32_t mask = upb_FromBase92(ch);
       for (int i = 0; i < 5; i++, base++, mask >>= 1) {
-        if (mask & 1) {
-          if (!upb_MiniTable_BuildEnumValue(&d, table, base, arena)) {
-            return NULL;
-          }
-        }
+        if (mask & 1) upb_MiniTable_BuildEnumValue(&d, base);
       }
     } else if (kUpb_EncodedValue_MinSkip <= ch &&
                ch <= kUpb_EncodedValue_MaxSkip) {
@@ -1097,7 +1127,7 @@
     }
   }
 
-  return table;
+  return d.enum_table;
 }
 
 const char* upb_MiniTable_BuildExtension(const char* data, size_t len,
diff --git a/upb/mini_table.h b/upb/mini_table.h
index d71ebcf..0e25995 100644
--- a/upb/mini_table.h
+++ b/upb/mini_table.h
@@ -50,19 +50,6 @@
   return mini_table->subs[field->submsg_index].subenum;
 }
 
-// Validates enum value against range defined by enum mini table.
-UPB_INLINE bool upb_MiniTable_Enum_CheckValue(const upb_MiniTable_Enum* e,
-                                              int32_t val) {
-  uint32_t uval = (uint32_t)val;
-  if (uval < 64) return e->mask & (1ULL << uval);
-  // OPT: binary search long lists?
-  int n = e->value_count;
-  for (int i = 0; i < n; i++) {
-    if (e->values[i] == val) return true;
-  }
-  return false;
-}
-
 /** upb_MtDataEncoder *********************************************************/
 
 // Functions to encode a string in a format that can be loaded by
diff --git a/upb/msg_internal.h b/upb/msg_internal.h
index 8c18a86..650cecb 100644
--- a/upb/msg_internal.h
+++ b/upb/msg_internal.h
@@ -137,11 +137,47 @@
 } _upb_FastTable_Entry;
 
 typedef struct {
-  const int32_t* values;  // List of values <0 or >63
-  uint64_t mask;          // Bits are set for acceptable value 0 <= x < 64
-  int value_count;
+  uint32_t mask_limit;   // Limit enum value that can be tested with mask.
+  uint32_t value_count;  // Number of values after the bitfield.
+  uint32_t data[];       // Bitmask + enumerated values follow.
 } upb_MiniTable_Enum;
 
+typedef enum {
+  _kUpb_FastEnumCheck_ValueIsInEnum = 0,
+  _kUpb_FastEnumCheck_ValueIsNotInEnum = 1,
+  _kUpb_FastEnumCheck_CannotCheckFast = 2,
+} _kUpb_FastEnumCheck_Status;
+
+UPB_INLINE _kUpb_FastEnumCheck_Status
+_upb_MiniTable_CheckEnumValueFast(const upb_MiniTable_Enum* e, uint32_t val) {
+  if (UPB_UNLIKELY(val >= 64)) return _kUpb_FastEnumCheck_CannotCheckFast;
+  uint64_t mask = e->data[0] | ((uint64_t)e->data[1] << 32);
+  return (mask & (1ULL << val)) ? _kUpb_FastEnumCheck_ValueIsInEnum
+                                : _kUpb_FastEnumCheck_ValueIsNotInEnum;
+}
+
+UPB_INLINE bool _upb_MiniTable_CheckEnumValueSlow(const upb_MiniTable_Enum* e,
+                                                  uint32_t val) {
+  if (val < e->mask_limit) return e->data[val / 32] & (1ULL << (val % 32));
+  // OPT: binary search long lists?
+  const uint32_t* start = &e->data[e->mask_limit / 32];
+  const uint32_t* limit = &e->data[(e->mask_limit / 32) + e->value_count];
+  for (const uint32_t* p = start; p < limit; p++) {
+    if (*p == val) return true;
+  }
+  return false;
+}
+
+// Validates enum value against range defined by enum mini table.
+UPB_INLINE bool upb_MiniTable_Enum_CheckValue(const upb_MiniTable_Enum* e,
+                                              uint32_t val) {
+  _kUpb_FastEnumCheck_Status status = _upb_MiniTable_CheckEnumValueFast(e, val);
+  if (UPB_UNLIKELY(status == _kUpb_FastEnumCheck_CannotCheckFast)) {
+    return _upb_MiniTable_CheckEnumValueSlow(e, val);
+  }
+  return status == _kUpb_FastEnumCheck_ValueIsInEnum ? true : false;
+}
+
 typedef union {
   const struct upb_MiniTable* submsg;
   const upb_MiniTable_Enum* subenum;
diff --git a/upbc/protoc-gen-upb.cc b/upbc/protoc-gen-upb.cc
index 24ac89d..11c6092 100644
--- a/upbc/protoc-gen-upb.cc
+++ b/upbc/protoc-gen-upb.cc
@@ -1373,16 +1373,13 @@
 
 void WriteEnum(const upb_MiniTable_Enum* mt, const protobuf::EnumDescriptor* e,
                Output& output) {
-  std::string values_init = "NULL";
-
-  if (mt->value_count) {
-    values_init = EnumInit(e) + "_values";
-    output("static const int32_t $0[$1] = {\n", values_init, mt->value_count);
-    for (int i = 0; i < mt->value_count; i++) {
-      output("  $0,\n", mt->values[i]);
-    }
-    output("};\n\n");
+  std::string values_init = "{\n";
+  uint32_t value_count = (mt->mask_limit / 32) + mt->value_count;
+  for (uint32_t i = 0; i < value_count; i++) {
+    absl::StrAppend(&values_init, "                0x", absl::Hex(mt->data[i]),
+                    ",\n");
   }
+  values_init += "    }";
 
   output(
       R"cc(
@@ -1392,8 +1389,7 @@
             $3,
         };
       )cc",
-      EnumInit(e), values_init, absl::StrCat("0x", absl::Hex(mt->mask), "ULL"),
-      mt->value_count);
+      EnumInit(e), mt->mask_limit, mt->value_count, values_init);
   output("\n");
 }