Extern "C" custom-allocator declerations
diff --git a/src/hb-private.hh b/src/hb-private.hh
index 165cd0d..be29391 100644
--- a/src/hb-private.hh
+++ b/src/hb-private.hh
@@ -60,10 +60,10 @@
&& defined(hb_calloc_impl) \
&& defined(hb_realloc_impl) \
&& defined(hb_free_impl)
-extern void* hb_malloc_impl(size_t size);
-extern void* hb_calloc_impl(size_t nmemb, size_t size);
-extern void* hb_realloc_impl(void *ptr, size_t size);
-extern void hb_free_impl(void *ptr);
+extern "C" void* hb_malloc_impl(size_t size);
+extern "C" void* hb_calloc_impl(size_t nmemb, size_t size);
+extern "C" void* hb_realloc_impl(void *ptr, size_t size);
+extern "C" void hb_free_impl(void *ptr);
#define malloc hb_malloc_impl
#define calloc hb_calloc_impl
#define realloc hb_realloc_impl
