diff --git a/CMakeLists.txt b/CMakeLists.txt
index 6a1c97f75..c1517e93c 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -242,7 +242,7 @@ IF ((CMAKE_C_COMPILER_ID MATCHES "GNU") AND NOT CMAKE_COMPILER_IS_MINGW)
     SET(CMAKE_C_FLAGS "-fPIC ${CMAKE_C_FLAGS}")
   ENDIF()
   # hide all not-exported symbols
-  SET(CMAKE_CXX_FLAGS "-g -fvisibility=hidden -fno-strict-aliasing -Wall -O3 ${CMAKE_CXX_FLAGS}")
+  SET(CMAKE_CXX_FLAGS "-g -fvisibility=hidden -fno-strict-aliasing -Wall ${CMAKE_CXX_FLAGS}")
   SET(CMAKE_C_FLAGS "-fno-strict-aliasing ${CMAKE_C_FLAGS}")
   SET(LIBSTDC++_LIBRARIES -lstdc++)
 ELSEIF(MSVC)
@@ -259,7 +259,7 @@ ELSEIF ( "${CMAKE_CXX_COMPILER_ID}" MATCHES "Clang" )
     SET(CMAKE_CXX_FLAGS "-fPIC -std=c++11 ${CMAKE_CXX_FLAGS}")
     SET(CMAKE_C_FLAGS "-fPIC ${CMAKE_C_FLAGS}")
   ENDIF()
-  SET(CMAKE_CXX_FLAGS "-g -fvisibility=hidden -fno-strict-aliasing -Wall -O3 -Wno-long-long ${CMAKE_CXX_FLAGS}" )
+  SET(CMAKE_CXX_FLAGS "-g -fvisibility=hidden -fno-strict-aliasing -Wall -Wno-long-long ${CMAKE_CXX_FLAGS}" )
   SET(CMAKE_C_FLAGS "-fno-strict-aliasing ${CMAKE_C_FLAGS}")
 ELSEIF( CMAKE_COMPILER_IS_MINGW )
   IF (CMAKE_CXX_COMPILER_VERSION VERSION_LESS 7.0)