diff --git a/src/winio.c b/src/winio.c
index 8da48ebaacec88a1ce924fb45d0c4bbc3f5ecacc..e2487bf18a92dc7c61b77bc0799c66832f8e654b 100644
--- a/src/winio.c
+++ b/src/winio.c
@@ -4144,7 +4144,7 @@ int check_linenumbers(const filestruct *fileptr)
 
     return check_line;
 }
-#endif
+#endif /* !NDEBUG */
 
 #ifdef DEBUG
 /* Dump the filestruct inptr to stderr. */