diff --git a/dlib/dnn/cuda_dlib.h b/dlib/dnn/cuda_dlib.h
index 39f1bb943..a5c0ea0b6 100644
--- a/dlib/dnn/cuda_dlib.h
+++ b/dlib/dnn/cuda_dlib.h
@@ -141,7 +141,7 @@ namespace dlib
         ){}
 
         inline int get_device (
-        ){}
+        ){ return 0; }
 
 #endif // DLIB_USE_CUDA