diff --git a/dlib/test/is_same_object.cpp b/dlib/test/is_same_object.cpp
index a700e5f34..d915eb95d 100644
--- a/dlib/test/is_same_object.cpp
+++ b/dlib/test/is_same_object.cpp
@@ -37,7 +37,7 @@ namespace
 
         void funct(int) {}
 
-        float funct_f(int) {}
+        float funct_f(int) { return 0;}
     };
 
     void test_metaprog()