diff --git a/reactos/lib/sdk/crt/include/internal/mingw-w64/internal.h b/reactos/lib/sdk/crt/include/internal/mingw-w64/internal.h
index f3f9c18e006..5983a7cab51 100644
--- a/reactos/lib/sdk/crt/include/internal/mingw-w64/internal.h
+++ b/reactos/lib/sdk/crt/include/internal/mingw-w64/internal.h
@@ -18,6 +18,7 @@ extern "C" {
 
 #ifdef __REACTOS__
 #include "malloc.h"
+struct _exception;
 __declspec(dllimport) void __setusermatherr(int (__cdecl *)(struct _exception *));
 #define __mingw_fprintf fprintf
 #define __mingw_vfprintf vfprintf