diff --git a/protocol.c b/protocol.c
index 5e636785d1..9741f05750 100644
--- a/protocol.c
+++ b/protocol.c
@@ -17,6 +17,10 @@ static enum protocol_version parse_protocol_version(const char *value)
 enum protocol_version get_protocol_version_config(void)
 {
 	const char *value;
+	enum protocol_version retval = protocol_v0;
+	const char *git_test_k = "GIT_TEST_PROTOCOL_VERSION";
+	const char *git_test_v = getenv(git_test_k);
+
 	if (!git_config_get_string_const("protocol.version", &value)) {
 		enum protocol_version version = parse_protocol_version(value);
 
@@ -24,10 +28,19 @@ enum protocol_version get_protocol_version_config(void)
 			die("unknown value for config 'protocol.version': %s",
 			    value);
 
-		return version;
+		retval = version;
 	}
 
-	return protocol_v0;
+	if (git_test_v && *git_test_v) {
+		enum protocol_version env = parse_protocol_version(git_test_v);
+
+		if (env == protocol_unknown_version)
+			die("unknown value for %s: %s", git_test_k, git_test_v);
+		if (retval < env)
+			retval = env;
+	}
+
+	return retval;
 }
 
 enum protocol_version determine_protocol_version_server(void)
diff --git a/t/README b/t/README
index 25864ec883..21e941eb94 100644
--- a/t/README
+++ b/t/README
@@ -327,6 +327,9 @@ marked strings" in po/README for details.
 GIT_TEST_SPLIT_INDEX=<boolean> forces split-index mode on the whole
 test suite. Accept any boolean values that are accepted by git-config.
 
+GIT_TEST_PROTOCOL_VERSION=<n>, when set, overrides the
+'protocol.version' setting to n if it is less than n.
+
 GIT_TEST_FULL_IN_PACK_ARRAY=<boolean> exercises the uncommon
 pack-objects code path where there are more than 1024 packs even if
 the actual number of packs in repository is below this limit. Accept
diff --git a/t/t5400-send-pack.sh b/t/t5400-send-pack.sh
index f1932ea431..571d620aed 100755
--- a/t/t5400-send-pack.sh
+++ b/t/t5400-send-pack.sh
@@ -288,7 +288,7 @@ test_expect_success 'receive-pack de-dupes .have lines' '
 	$shared .have
 	EOF
 
-	GIT_TRACE_PACKET=$(pwd)/trace \
+	GIT_TRACE_PACKET=$(pwd)/trace GIT_TEST_PROTOCOL_VERSION= \
 	    git push \
 		--receive-pack="unset GIT_TRACE_PACKET; git-receive-pack" \
 		fork HEAD:foo &&
diff --git a/t/t5551-http-fetch-smart.sh b/t/t5551-http-fetch-smart.sh
index 8630b0cc39..f7a84f3003 100755
--- a/t/t5551-http-fetch-smart.sh
+++ b/t/t5551-http-fetch-smart.sh
@@ -43,7 +43,8 @@ test_expect_success 'clone http repository' '
 	< Cache-Control: no-cache, max-age=0, must-revalidate
 	< Content-Type: application/x-git-upload-pack-result
 	EOF
-	GIT_TRACE_CURL=true git clone --quiet $HTTPD_URL/smart/repo.git clone 2>err &&
+	GIT_TRACE_CURL=true GIT_TEST_PROTOCOL_VERSION= \
+		git clone --quiet $HTTPD_URL/smart/repo.git clone 2>err &&
 	test_cmp file clone/file &&
 	tr '\''\015'\'' Q <err |
 	sed -e "