diff --git a/src/dirname.c b/src/dirname.c
index 2e4a26b..0f75514 100644
--- a/src/dirname.c
+++ b/src/dirname.c
@@ -8,6 +8,6 @@ main(int argc, char *argv[]) {
     fprintf(stderr, "%s", argv[0]);
     return 1;
   }
-  puts(dir);
+  printf("%s/\n", dir); /* Trailing slash because POSIX */
   return 0;
 }