diff --git a/gtsam/base/Manifold.h b/gtsam/base/Manifold.h
index b20c60822..d7ea9ea4c 100644
--- a/gtsam/base/Manifold.h
+++ b/gtsam/base/Manifold.h
@@ -138,7 +138,7 @@ class IsManifold {
 public:
 
   typedef typename traits<T>::structure_category structure_category_tag;
-  static const size_t dim = traits<T>::dimension;
+  static const int dim = traits<T>::dimension;
   typedef typename traits<T>::ManifoldType ManifoldType;
   typedef typename traits<T>::TangentVector TangentVector;