diff --git a/src/flex-scanner.h b/src/flex-scanner.h
index f27938dc..99798411 100644
--- a/src/flex-scanner.h
+++ b/src/flex-scanner.h
@@ -82,16 +82,16 @@ int   FLEX_PREFIX (lex_destroy) (void);
 
 static struct obstack obstack_for_string;
 
-#define STRING_GROW   \
+# define STRING_GROW   \
   obstack_grow (&obstack_for_string, yytext, yyleng)
 
-#define STRING_FINISH					\
+# define STRING_FINISH					\
   do {							\
     obstack_1grow (&obstack_for_string, '\0');		\
     last_string = obstack_finish (&obstack_for_string);	\
   } while (0)
 
-#define STRING_FREE \
+# define STRING_FREE \
   obstack_free (&obstack_for_string, last_string)
 
 #endif