diff --git a/src/hb-common.h b/src/hb-common.h
index 78bc43c12..1728db711 100644
--- a/src/hb-common.h
+++ b/src/hb-common.h
@@ -33,6 +33,7 @@
 #ifndef HB_COMMON_H
 #define HB_COMMON_H
 
+#ifndef HB_BEGIN_DECLS
 # ifdef __cplusplus
 #  define HB_BEGIN_DECLS	extern "C" {
 #  define HB_END_DECLS		}
@@ -40,6 +41,7 @@
 #  define HB_BEGIN_DECLS
 #  define HB_END_DECLS
 # endif /* !__cplusplus */
+#endif
 
 HB_BEGIN_DECLS