diff --git a/win32/Makefile.sub b/win32/Makefile.sub
index 35d60190f1..d32f655317 100644
--- a/win32/Makefile.sub
+++ b/win32/Makefile.sub
@@ -749,7 +749,7 @@ $(CONFIG_H): $(MKFILES) $(srcdir)/win32/Makefile.sub $(win_srcdir)/Makefile.sub
 !if "$(EXTSTATIC)" == "static"
 #define EXTSTATIC 1
 !endif
-#define EXPORT_PREFIX " "
+#define EXPORT_PREFIX "_"
 #define EXECUTABLE_EXTS $(EXECUTABLE_EXTS)
 #define RUBY_COREDLL "$(RT)"
 #define LIBRUBY_SO "$(LIBRUBY_SO)"