diff --git a/builtin/diff.c b/builtin/diff.c
index 4326fa56bf..7b9917b03e 100644
--- a/builtin/diff.c
+++ b/builtin/diff.c
@@ -341,7 +341,7 @@ int cmd_diff(int argc, const char **argv, const char *prefix)
 	}
 	if (no_index)
 		/* If this is a no-index diff, just run it and exit there. */
-		diff_no_index(&rev, argc, argv, prefix);
+		diff_no_index(&rev, argc, argv);
 
 	/* Otherwise, we are doing the usual "git" diff */
 	rev.diffopt.skip_stat_unmatch = !!diff_auto_refresh_index;
diff --git a/diff-no-index.c b/diff-no-index.c
index 0320605a84..8edc6f3690 100644
--- a/diff-no-index.c
+++ b/diff-no-index.c
@@ -239,12 +239,12 @@ static void fixup_paths(const char **path, struct strbuf *replacement)
 }
 
 void diff_no_index(struct rev_info *revs,
-		   int argc, const char **argv,
-		   const char *prefix)
+		   int argc, const char **argv)
 {
 	int i, prefixlen;
 	const char *paths[2];
 	struct strbuf replacement = STRBUF_INIT;
+	const char *prefix = revs->prefix;
 
 	diff_setup(&revs->diffopt);
 	for (i = 1; i < argc - 2; ) {
diff --git a/diff.h b/diff.h
index f7208ad103..f61ee5494b 100644
--- a/diff.h
+++ b/diff.h
@@ -345,7 +345,7 @@ extern int diff_flush_patch_id(struct diff_options *, unsigned char *);
 
 extern int diff_result_code(struct diff_options *, int);
 
-extern void diff_no_index(struct rev_info *, int, const char **, const char *);
+extern void diff_no_index(struct rev_info *, int, const char **);
 
 extern int index_differs_from(const char *def, int diff_flags);