diff --git a/builtin/submodule--helper.c b/builtin/submodule--helper.c
index 79044ae53d..98f303f5fa 100644
--- a/builtin/submodule--helper.c
+++ b/builtin/submodule--helper.c
@@ -127,7 +127,8 @@ static int module_name(int argc, const char **argv, const char *prefix)
  */
 static int submodule_config_ok(const char *var)
 {
-	if (starts_with(var, "credential."))
+	if (starts_with(var, "credential.") ||
+	    (starts_with(var, "http.") && ends_with(var, ".extraheader")))
 		return 1;
 	return 0;
 }
diff --git a/t/t5551-http-fetch-smart.sh b/t/t5551-http-fetch-smart.sh
index e44fe72c7a..179416818d 100755
--- a/t/t5551-http-fetch-smart.sh
+++ b/t/t5551-http-fetch-smart.sh
@@ -286,7 +286,16 @@ test_expect_success 'custom http headers' '
 	test_must_fail git fetch "$HTTPD_URL/smart_headers/repo.git" &&
 	git -c http.extraheader="x-magic-one: abra" \
 	    -c http.extraheader="x-magic-two: cadabra" \
-	    fetch "$HTTPD_URL/smart_headers/repo.git"
+	    fetch "$HTTPD_URL/smart_headers/repo.git" &&
+	git update-index --add --cacheinfo 160000,$(git rev-parse HEAD),sub &&
+	git config -f .gitmodules submodule.sub.path sub &&
+	git config -f .gitmodules submodule.sub.url \
+		"$HTTPD_URL/smart_headers/repo.git" &&
+	git submodule init sub &&
+	test_must_fail git submodule update sub &&
+	git -c http.extraheader="x-magic-one: abra" \
+	    -c http.extraheader="x-magic-two: cadabra" \
+		submodule update sub
 '
 
 stop_httpd