diff --git a/src/parse-gram.c b/src/parse-gram.c
index 4f42db28..c468acfc 100644
--- a/src/parse-gram.c
+++ b/src/parse-gram.c
@@ -1851,7 +1851,7 @@ yyerrlab:
 	      }
 
 	  yyf = _(yyformat);
-	  yysize1 = yysize + strlen (yyf);
+	  yysize1 = yysize + yystrlen (yyf);
 	  yysize_overflow |= yysize1 < yysize;
 	  yysize = yysize1;