diff --git a/src/Makefile.am b/src/Makefile.am
index 9f60d26..ea2c294 100644
--- a/src/Makefile.am
+++ b/src/Makefile.am
@@ -13,14 +13,14 @@
 	hb-font.c \
 	hb-font-private.h \
 	hb-private.h \
-	hb-open-file-private.h \
-	hb-open-types-private.h \
+	hb-open-file-private.hh \
+	hb-open-types-private.hh \
 	hb-ot-layout.cc \
-	hb-ot-layout-common-private.h \
-	hb-ot-layout-gdef-private.h \
-	hb-ot-layout-gpos-private.h \
-	hb-ot-layout-gsubgpos-private.h \
-	hb-ot-layout-gsub-private.h \
+	hb-ot-layout-common-private.hh \
+	hb-ot-layout-gdef-private.hh \
+	hb-ot-layout-gpos-private.hh \
+	hb-ot-layout-gsubgpos-private.hh \
+	hb-ot-layout-gsub-private.hh \
 	hb-ot-layout-private.h \
 	hb-object-private.h \
 	$(NULL)
diff --git a/src/hb-open-file-private.h b/src/hb-open-file-private.hh
similarity index 96%
rename from src/hb-open-file-private.h
rename to src/hb-open-file-private.hh
index 9838288..c06bb88 100644
--- a/src/hb-open-file-private.h
+++ b/src/hb-open-file-private.hh
@@ -24,10 +24,10 @@
  * Red Hat Author(s): Behdad Esfahbod
  */
 
-#ifndef HB_OPEN_FILE_PRIVATE_H
-#define HB_OPEN_FILE_PRIVATE_H
+#ifndef HB_OPEN_FILE_PRIVATE_HH
+#define HB_OPEN_FILE_PRIVATE_HH
 
-#include "hb-open-types-private.h"
+#include "hb-open-types-private.hh"
 
 
 /*
@@ -142,4 +142,4 @@
 ASSERT_SIZE (OpenTypeFontFile, 4);
 
 
-#endif /* HB_OPEN_FILE_PRIVATE_H */
+#endif /* HB_OPEN_FILE_PRIVATE_HH */
diff --git a/src/hb-open-types-private.h b/src/hb-open-types-private.hh
similarity index 98%
rename from src/hb-open-types-private.h
rename to src/hb-open-types-private.hh
index 051853e..98efde4 100644
--- a/src/hb-open-types-private.h
+++ b/src/hb-open-types-private.hh
@@ -24,8 +24,8 @@
  * Red Hat Author(s): Behdad Esfahbod
  */
 
-#ifndef HB_OPEN_TYPES_PRIVATE_H
-#define HB_OPEN_TYPES_PRIVATE_H
+#ifndef HB_OPEN_TYPES_PRIVATE_HH
+#define HB_OPEN_TYPES_PRIVATE_HH
 
 #include "hb-private.h"
 
@@ -383,4 +383,4 @@
   }
 
 
-#endif /* HB_OPEN_TYPES_PRIVATE_H */
+#endif /* HB_OPEN_TYPES_PRIVATE_HH */
diff --git a/src/hb-ot-layout-common-private.h b/src/hb-ot-layout-common-private.hh
similarity index 98%
rename from src/hb-ot-layout-common-private.h
rename to src/hb-ot-layout-common-private.hh
index b3e2a00..6f66118 100644
--- a/src/hb-ot-layout-common-private.h
+++ b/src/hb-ot-layout-common-private.hh
@@ -24,12 +24,12 @@
  * Red Hat Author(s): Behdad Esfahbod
  */
 
-#ifndef HB_OT_LAYOUT_COMMON_PRIVATE_H
-#define HB_OT_LAYOUT_COMMON_PRIVATE_H
+#ifndef HB_OT_LAYOUT_COMMON_PRIVATE_HH
+#define HB_OT_LAYOUT_COMMON_PRIVATE_HH
 
 #include "hb-ot-layout-private.h"
 
-#include "hb-open-types-private.h"
+#include "hb-open-types-private.hh"
 
 
 /*
@@ -444,4 +444,4 @@
 ASSERT_SIZE (Device, 6);
 
 
-#endif /* HB_OT_LAYOUT_COMMON_PRIVATE_H */
+#endif /* HB_OT_LAYOUT_COMMON_PRIVATE_HH */
diff --git a/src/hb-ot-layout-gdef-private.h b/src/hb-ot-layout-gdef-private.hh
similarity index 97%
rename from src/hb-ot-layout-gdef-private.h
rename to src/hb-ot-layout-gdef-private.hh
index 0ed74a8..b890099 100644
--- a/src/hb-ot-layout-gdef-private.h
+++ b/src/hb-ot-layout-gdef-private.hh
@@ -24,10 +24,10 @@
  * Red Hat Author(s): Behdad Esfahbod
  */
 
-#ifndef HB_OT_LAYOUT_GDEF_PRIVATE_H
-#define HB_OT_LAYOUT_GDEF_PRIVATE_H
+#ifndef HB_OT_LAYOUT_GDEF_PRIVATE_HH
+#define HB_OT_LAYOUT_GDEF_PRIVATE_HH
 
-#include "hb-ot-layout-common-private.h"
+#include "hb-ot-layout-common-private.hh"
 
 
 struct GlyphClassDef : ClassDef
@@ -317,4 +317,4 @@
 ASSERT_SIZE (GDEF, 12);
 
 
-#endif /* HB_OT_LAYOUT_GDEF_PRIVATE_H */
+#endif /* HB_OT_LAYOUT_GDEF_PRIVATE_HH */
diff --git a/src/hb-ot-layout-gpos-private.h b/src/hb-ot-layout-gpos-private.hh
similarity index 99%
rename from src/hb-ot-layout-gpos-private.h
rename to src/hb-ot-layout-gpos-private.hh
index 8bb3f95..8611848 100644
--- a/src/hb-ot-layout-gpos-private.h
+++ b/src/hb-ot-layout-gpos-private.hh
@@ -24,10 +24,10 @@
  * Red Hat Author(s): Behdad Esfahbod
  */
 
-#ifndef HB_OT_LAYOUT_GPOS_PRIVATE_H
-#define HB_OT_LAYOUT_GPOS_PRIVATE_H
+#ifndef HB_OT_LAYOUT_GPOS_PRIVATE_HH
+#define HB_OT_LAYOUT_GPOS_PRIVATE_HH
 
-#include "hb-ot-layout-gsubgpos-private.h"
+#include "hb-ot-layout-gsubgpos-private.hh"
 
 #define HB_OT_LAYOUT_GPOS_NO_LAST ((unsigned int) -1)
 
@@ -1352,4 +1352,4 @@
 }
 
 
-#endif /* HB_OT_LAYOUT_GPOS_PRIVATE_H */
+#endif /* HB_OT_LAYOUT_GPOS_PRIVATE_HH */
diff --git a/src/hb-ot-layout-gsub-private.h b/src/hb-ot-layout-gsub-private.hh
similarity index 98%
rename from src/hb-ot-layout-gsub-private.h
rename to src/hb-ot-layout-gsub-private.hh
index e4c3afb..38aa24b 100644
--- a/src/hb-ot-layout-gsub-private.h
+++ b/src/hb-ot-layout-gsub-private.hh
@@ -24,10 +24,10 @@
  * Red Hat Author(s): Behdad Esfahbod
  */
 
-#ifndef HB_OT_LAYOUT_GSUB_PRIVATE_H
-#define HB_OT_LAYOUT_GSUB_PRIVATE_H
+#ifndef HB_OT_LAYOUT_GSUB_PRIVATE_HH
+#define HB_OT_LAYOUT_GSUB_PRIVATE_HH
 
-#include "hb-ot-layout-gsubgpos-private.h"
+#include "hb-ot-layout-gsubgpos-private.hh"
 
 
 struct SingleSubstFormat1
@@ -748,4 +748,4 @@
 }
 
 
-#endif /* HB_OT_LAYOUT_GSUB_PRIVATE_H */
+#endif /* HB_OT_LAYOUT_GSUB_PRIVATE_HH */
diff --git a/src/hb-ot-layout-gsubgpos-private.h b/src/hb-ot-layout-gsubgpos-private.hh
similarity index 98%
rename from src/hb-ot-layout-gsubgpos-private.h
rename to src/hb-ot-layout-gsubgpos-private.hh
index 35d8f8c..7a37509 100644
--- a/src/hb-ot-layout-gsubgpos-private.h
+++ b/src/hb-ot-layout-gsubgpos-private.hh
@@ -24,11 +24,11 @@
  * Red Hat Author(s): Behdad Esfahbod
  */
 
-#ifndef HB_OT_LAYOUT_GSUBGPOS_PRIVATE_H
-#define HB_OT_LAYOUT_GSUBGPOS_PRIVATE_H
+#ifndef HB_OT_LAYOUT_GSUBGPOS_PRIVATE_HH
+#define HB_OT_LAYOUT_GSUBGPOS_PRIVATE_HH
 
 #include "hb-buffer-private.h"
-#include "hb-ot-layout-gdef-private.h"
+#include "hb-ot-layout-gdef-private.hh"
 
 
 #define APPLY_ARG_DEF \
@@ -770,4 +770,4 @@
 ASSERT_SIZE (GSUBGPOS, 10);
 
 
-#endif /* HB_OT_LAYOUT_GSUBGPOS_PRIVATE_H */
+#endif /* HB_OT_LAYOUT_GSUBGPOS_PRIVATE_HH */
diff --git a/src/hb-ot-layout.cc b/src/hb-ot-layout.cc
index 82ceaee..46517fa 100644
--- a/src/hb-ot-layout.cc
+++ b/src/hb-ot-layout.cc
@@ -30,10 +30,10 @@
 
 #include "hb-ot-layout-private.h"
 
-#include "hb-open-file-private.h"
-#include "hb-ot-layout-gdef-private.h"
-#include "hb-ot-layout-gsub-private.h"
-#include "hb-ot-layout-gpos-private.h"
+#include "hb-open-file-private.hh"
+#include "hb-ot-layout-gdef-private.hh"
+#include "hb-ot-layout-gsub-private.hh"
+#include "hb-ot-layout-gpos-private.hh"
 
 
 #include <stdlib.h>
diff --git a/src/main.cc b/src/main.cc
index 25720c8..8d76694 100644
--- a/src/main.cc
+++ b/src/main.cc
@@ -25,9 +25,9 @@
  */
 
 #define HB_OT_LAYOUT_CC
-#include "hb-open-file-private.h"
-#include "hb-ot-layout-gdef-private.h"
-#include "hb-ot-layout-gsubgpos-private.h"
+#include "hb-open-file-private.hh"
+#include "hb-ot-layout-gdef-private.hh"
+#include "hb-ot-layout-gsubgpos-private.hh"
 
 #include <glib.h>
 #include <stdlib.h>