diff --git a/src/util.h b/src/util.h
index 97d638c9..60e99431 100644
--- a/src/util.h
+++ b/src/util.h
@@ -599,6 +599,7 @@ public:
     T median() const
     {
         int size = vSorted.size();
+        assert(size>0);
         if(size & 1) // Odd number of elements
         {
             return vSorted[size/2];