diff --git a/src/programs/unit_tests/ExactlyOnceTests.h b/src/programs/unit_tests/ExactlyOnceTests.h
index f59459f7e..9644b85ec 100644
--- a/src/programs/unit_tests/ExactlyOnceTests.h
+++ b/src/programs/unit_tests/ExactlyOnceTests.h
@@ -45,6 +45,9 @@ struct SimpleProcessor : public JEventProcessor {
         init_count += 1;
     }
 
+    void Process(const JEvent&) override {
+    }
+
     void Finish() override {
         finish_count += 1;
     }