diff --git a/diff.c b/diff.c
index 5388ded214..f4b58709eb 100644
--- a/diff.c
+++ b/diff.c
@@ -2913,9 +2913,8 @@ static void run_diff_cmd(const char *pgm,
 	int complete_rewrite = (p->status == DIFF_STATUS_MODIFIED) && p->score;
 	int must_show_header = 0;
 
-	if (!DIFF_OPT_TST(o, ALLOW_EXTERNAL))
-		pgm = NULL;
-	else {
+
+	if (DIFF_OPT_TST(o, ALLOW_EXTERNAL)) {
 		struct userdiff_driver *drv = userdiff_find_by_path(attr_path);
 		if (drv && drv->external)
 			pgm = drv->external;
@@ -2995,6 +2994,9 @@ static void run_diff(struct diff_filepair *p, struct diff_options *o)
 	if (o->prefix_length)
 		strip_prefix(o->prefix_length, &name, &other);
 
+	if (!DIFF_OPT_TST(o, ALLOW_EXTERNAL))
+		pgm = NULL;
+
 	if (DIFF_PAIR_UNMERGED(p)) {
 		run_diff_cmd(pgm, name, NULL, attr_path,
 			     NULL, NULL, NULL, o, p);
diff --git a/t/t4020-diff-external.sh b/t/t4020-diff-external.sh
index 083f62d1d6..025df533ca 100755
--- a/t/t4020-diff-external.sh
+++ b/t/t4020-diff-external.sh
@@ -48,7 +48,26 @@ test_expect_success 'GIT_EXTERNAL_DIFF environment and --no-ext-diff' '
 
 '
 
+test_expect_success SYMLINKS 'typechange diff' '
+	rm -f file &&
+	ln -s elif file &&
+	GIT_EXTERNAL_DIFF=echo git diff  | {
+		read path oldfile oldhex oldmode newfile newhex newmode &&
+		test "z$path" = zfile &&
+		test "z$oldmode" = z100644 &&
+		test "z$newhex" = "z$_z40" &&
+		test "z$newmode" = z120000 &&
+		oh=$(git rev-parse --verify HEAD:file) &&
+		test "z$oh" = "z$oldhex"
+	} &&
+	GIT_EXTERNAL_DIFF=echo git diff --no-ext-diff >actual &&
+	git diff >expect &&
+	test_cmp expect actual
+'
+
 test_expect_success 'diff attribute' '
+	git reset --hard &&
+	echo third >file &&
 
 	git config diff.parrot.command echo &&