diff --git a/diff.c b/diff.c
index ef7159968b..e71cf75886 100644
--- a/diff.c
+++ b/diff.c
@@ -4136,18 +4136,13 @@ static void prep_temp_blob(struct index_state *istate,
 			   int mode)
 {
 	struct strbuf buf = STRBUF_INIT;
-	struct strbuf tempfile = STRBUF_INIT;
 	char *path_dup = xstrdup(path);
 	const char *base = basename(path_dup);
 	struct checkout_metadata meta;
 
 	init_checkout_metadata(&meta, NULL, NULL, oid);
 
-	/* Generate "XXXXXX_basename.ext" */
-	strbuf_addstr(&tempfile, "XXXXXX_");
-	strbuf_addstr(&tempfile, base);
-
-	temp->tempfile = mks_tempfile_ts(tempfile.buf, strlen(base) + 1);
+	temp->tempfile = mks_tempfile_dt("git-blob-XXXXXX", base);
 	if (!temp->tempfile)
 		die_errno("unable to create temp-file");
 	if (convert_to_working_tree(istate, path,
@@ -4162,7 +4157,6 @@ static void prep_temp_blob(struct index_state *istate,
 	oid_to_hex_r(temp->hex, oid);
 	xsnprintf(temp->mode, sizeof(temp->mode), "%06o", mode);
 	strbuf_release(&buf);
-	strbuf_release(&tempfile);
 	free(path_dup);
 }
 
diff --git a/t/t4020-diff-external.sh b/t/t4020-diff-external.sh
index 1219f8bd4c..858a5522f9 100755
--- a/t/t4020-diff-external.sh
+++ b/t/t4020-diff-external.sh
@@ -206,17 +206,17 @@ test_expect_success 'GIT_EXTERNAL_DIFF path counter/total' '
 '
 
 test_expect_success 'GIT_EXTERNAL_DIFF generates pretty paths' '
+	test_when_finished "git rm -f file.ext" &&
 	touch file.ext &&
 	git add file.ext &&
 	echo with extension > file.ext &&
 
 	cat >expect <<-EOF &&
-	file.ext file $(git rev-parse --verify HEAD:file) 100644 file.ext $(test_oid zero) 100644
+	file.ext
 	EOF
 	GIT_EXTERNAL_DIFF=echo git diff file.ext >out &&
-	cut -d" " -f1,3- <out >actual &&
-	git update-index --force-remove file.ext &&
-	rm file.ext
+	basename $(cut -d" " -f2 <out) >actual &&
+	test_cmp expect actual
 '
 
 echo "#!$SHELL_PATH" >fake-diff.sh