Use unsigned enums for mask types
diff --git a/src/hb-buffer.h b/src/hb-buffer.h
index 87c4ce5..3086851 100644
--- a/src/hb-buffer.h
+++ b/src/hb-buffer.h
@@ -172,10 +172,10 @@
 
 
 typedef enum { /*< flags >*/
-  HB_BUFFER_FLAG_DEFAULT			= 0x00000000,
-  HB_BUFFER_FLAG_BOT				= 0x00000001, /* Beginning-of-text */
-  HB_BUFFER_FLAG_EOT				= 0x00000002, /* End-of-text */
-  HB_BUFFER_FLAG_PRESERVE_DEFAULT_IGNORABLES	= 0x00000004
+  HB_BUFFER_FLAG_DEFAULT			= 0x00000000u,
+  HB_BUFFER_FLAG_BOT				= 0x00000001u, /* Beginning-of-text */
+  HB_BUFFER_FLAG_EOT				= 0x00000002u, /* End-of-text */
+  HB_BUFFER_FLAG_PRESERVE_DEFAULT_IGNORABLES	= 0x00000004u
 } hb_buffer_flags_t;
 
 void
@@ -275,10 +275,10 @@
  */
 
 typedef enum { /*< flags >*/
-  HB_BUFFER_SERIALIZE_FLAG_DEFAULT		= 0x00000000,
-  HB_BUFFER_SERIALIZE_FLAG_NO_CLUSTERS		= 0x00000001,
-  HB_BUFFER_SERIALIZE_FLAG_NO_POSITIONS		= 0x00000002,
-  HB_BUFFER_SERIALIZE_FLAG_NO_GLYPH_NAMES	= 0x00000004
+  HB_BUFFER_SERIALIZE_FLAG_DEFAULT		= 0x00000000u,
+  HB_BUFFER_SERIALIZE_FLAG_NO_CLUSTERS		= 0x00000001u,
+  HB_BUFFER_SERIALIZE_FLAG_NO_POSITIONS		= 0x00000002u,
+  HB_BUFFER_SERIALIZE_FLAG_NO_GLYPH_NAMES	= 0x00000004u
 } hb_buffer_serialize_flags_t;
 
 typedef enum {