diff --git a/gtsam/base/Matrix.cpp b/gtsam/base/Matrix.cpp
index 92c9a525e..d9ab7d71c 100644
--- a/gtsam/base/Matrix.cpp
+++ b/gtsam/base/Matrix.cpp
@@ -695,7 +695,7 @@ Matrix expm(const Matrix& A, size_t K) {
 
 /* ************************************************************************* */
 Matrix Cayley(const Matrix& A) {
-  int n = A.cols();
+  size_t n = A.cols();
   assert(A.rows() == n);
 
   // original