diff --git a/src/flex-scanner.h b/src/flex-scanner.h
index c1459055..bf190afd 100644
--- a/src/flex-scanner.h
+++ b/src/flex-scanner.h
@@ -71,4 +71,4 @@ static struct obstack obstack_for_string;
   } while (0)
 
 #define STRING_FREE \
-  obstack_free (&obstack_for_string, FLEX_PREFIX (last_string))
+  obstack_free (&obstack_for_string, last_string)