diff --git a/copasi/bindings/swig/CVector.i b/copasi/bindings/swig/CVector.i
index dccb66a677..b1b3c5874a 100644
--- a/copasi/bindings/swig/CVector.i
+++ b/copasi/bindings/swig/CVector.i
@@ -85,7 +85,7 @@
       return (*self)[i];
     }
 
-    int size() const
+    size_t size() const
     {
       return self->size();
     }