diff --git a/dGame/dGameMessages/MissionMessages.cpp b/dGame/dGameMessages/MissionMessages.cpp
index f31791875..410c2d2f5 100644
--- a/dGame/dGameMessages/MissionMessages.cpp
+++ b/dGame/dGameMessages/MissionMessages.cpp
@@ -125,8 +125,12 @@ namespace GameMessages {
 	void MissionDialogueOK::Handle(Entity& entityRef, const SystemAddress& sysAddr) {
 		Entity* entity = &entityRef;
 		Entity* player = Game::entityManager->GetEntity(responder);
+		if (!player) {
+			LOG("MissionDialogueOK for mission %i from unknown responder %llu", missionID, responder);
+			return;
+		}
 
-		if (entity) entity->GetScript()->OnMissionDialogueOK(entity, player, missionID, iMissionState);
+		entity->GetScript()->OnMissionDialogueOK(entity, player, missionID, iMissionState);
 
 		// Get the player's mission component
 		MissionComponent* missionComponent = static_cast<MissionComponent*>(player->GetComponent(eReplicaComponentType::MISSION));
diff --git a/tests/dGameTests/dGameMessagesTests/MissionMessagesTests.cpp b/tests/dGameTests/dGameMessagesTests/MissionMessagesTests.cpp
index f6c591ca9..b68976946 100644
--- a/tests/dGameTests/dGameMessagesTests/MissionMessagesTests.cpp
+++ b/tests/dGameTests/dGameMessagesTests/MissionMessagesTests.cpp
@@ -266,3 +266,15 @@ TEST_F(MissionMessagesTests, GoldenBytes) {
 	task.updates = { 1.5f, 2.0f };
 	EXPECT_PACKET_EQ(FromHex("01 00 00 00 04 00 00 00 02 00 00 c0 3f 00 00 00 40"), Payload(task));
 }
+
+// Behaviour fix: a MissionDialogueOK naming a responder that does not exist used to dereference a null player.
+TEST_F(MissionMessagesTests, MissionDialogueOKWithUnknownResponderDoesNotCrash) {
+	Entity missionGiver(15, info);
+	GameMessages::MissionDialogueOK ok;
+	ok.bIsComplete = false;
+	ok.iMissionState = eMissionState::AVAILABLE;
+	ok.missionID = 1727;
+	ok.responder = 0x7777; // no such entity
+	ok.Handle(missionGiver, UNASSIGNED_SYSTEM_ADDRESS);
+	SUCCEED();
+}