diff --git a/Lib/csharp/std_vector.i b/Lib/csharp/std_vector.i
index 8cddf4c5d..b0485eba6 100644
--- a/Lib/csharp/std_vector.i
+++ b/Lib/csharp/std_vector.i
@@ -70,7 +70,7 @@
     set {
       if (value < size())
         throw new global::System.ArgumentOutOfRangeException("Capacity");
-      reserve((uint)value);
+      reserve(($typemap(cstype, size_t))value);
     }
   }