diff --git a/loolwsd/test/UnitPrefork.cpp b/loolwsd/test/UnitPrefork.cpp
index 8ed2b94fa..4bedaaacd 100644
--- a/loolwsd/test/UnitPrefork.cpp
+++ b/loolwsd/test/UnitPrefork.cpp
@@ -66,7 +66,7 @@ public:
         numPrefork = NumToPrefork;
     }
 
-    virtual bool filterChildMessage(const std::vector<char>& payload)
+    virtual bool filterChildMessage(const std::vector<char>& payload) override
     {
         const std::string memory = LOOLProtocol::getFirstLine(payload);
         if (!memory.compare(0,6,"Error:"))