diff --git a/gtsam_unstable/nonlinear/ceres_rotation.h b/gtsam_unstable/nonlinear/ceres_rotation.h
index 83627291c..b02c10211 100644
--- a/gtsam_unstable/nonlinear/ceres_rotation.h
+++ b/gtsam_unstable/nonlinear/ceres_rotation.h
@@ -47,6 +47,7 @@
 
 #include <algorithm>
 #include <cmath>
+#include <assert.h>
 #define DCHECK assert
 
 namespace ceres {