diff --git a/src/runtime/c/pgf/typechecker.h b/src/runtime/c/pgf/typechecker.h
index cf33ebca2..117c640f6 100644
--- a/src/runtime/c/pgf/typechecker.h
+++ b/src/runtime/c/pgf/typechecker.h
@@ -101,7 +101,10 @@ class PGF_INTERNAL_DECL PgfTypechecker {
     };
 
     PgfDBMarshaller db_m;
-    bool type_error(const char *fmt, ...) __attribute__ ((format (printf, 2, 3)));
+    bool type_error(const char *fmt, ...)
+#ifdef __GNUC__
+    __attribute__ ((format (printf, 2, 3)));
+#endif
 
 public:
     PgfTypechecker(ref<PgfPGF> gr, PgfMarshaller *m, PgfUnmarshaller *u, PgfExn* err);