diff --git a/CMakeLists.txt b/CMakeLists.txt
index 83a5fe2..ca62a9f 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -443,7 +443,7 @@
 
     # Mac OS X
     IF (${CMAKE_SYSTEM_NAME} MATCHES "Darwin")
-      SET (CERES_CXX_FLAGS "${CERES_CXX_FLAGS} -fast")
+      SET (CERES_CXX_FLAGS "${CERES_CXX_FLAGS} -fast -msse3")
     ENDIF (${CMAKE_SYSTEM_NAME} MATCHES "Darwin")
   ENDIF (CMAKE_COMPILER_IS_GNUCXX)
   SET (CMAKE_CXX_FLAGS_RELEASE "${CMAKE_CXX_FLAGS_RELEASE} ${CERES_CXX_FLAGS}"