diff --git a/submodule.c b/submodule.c
index 5a62aa2..be29b34 100644
--- a/submodule.c
+++ b/submodule.c
@@ -475,7 +475,8 @@ void show_submodule_inline_diff(FILE *f, const char *path,
 	cp.no_stdin = 1;
 
 	/* TODO: other options may need to be passed here. */
-	argv_array_push(&cp.args, "diff");
+	argv_array_pushl(&cp.args, "diff", "--submodule=diff", NULL);
+
 	argv_array_pushf(&cp.args, "--line-prefix=%s", line_prefix);
 	if (DIFF_OPT_TST(o, REVERSE_DIFF)) {
 		argv_array_pushf(&cp.args, "--src-prefix=%s%s/",