index f0efdf425..4cd461986 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -194,7 +194,7 @@ set(CMAKE_CXX_FLAGS_DEBUG          "-DLEAN_DEBUG -DLEAN_TRACE")
 set(CMAKE_CXX_FLAGS_MINSIZEREL     "-DNDEBUG")
 set(CMAKE_CXX_FLAGS_RELEASE        "-DNDEBUG")
 set(CMAKE_CXX_FLAGS_RELWITHDEBINFO "-DLEAN_DEBUG")
-set(CMAKE_CXX_FLAGS_GPROF          "-O2 -g -pg")
+set(CMAKE_CXX_FLAGS_GPROF          "-g -pg")
 
 # OSX .dmg generation (this is working in progress)
 set(CPACK_DMG_BACKGROUND_IMAGE "${LEAN_SOURCE_DIR}/../images/lean.png")
@@ -264,8 +264,8 @@ if (NOT MSVC)
     set(CMAKE_CXX_FLAGS                "-Wall -Wextra -std=c++11 ${CMAKE_CXX_FLAGS}")
     set(CMAKE_CXX_FLAGS_DEBUG          "-g3 ${CMAKE_CXX_FLAGS_DEBUG}")
     set(CMAKE_CXX_FLAGS_MINSIZEREL     "-Os ${CMAKE_CXX_FLAGS_MINSIZEREL}")
-    set(CMAKE_CXX_FLAGS_RELEASE        "-O3 ${CMAKE_CXX_FLAGS_RELEASE}")
-    set(CMAKE_CXX_FLAGS_RELWITHDEBINFO "-O2 -g3 ${CMAKE_CXX_FLAGS_RELWITHDEBINFO}")
+    set(CMAKE_CXX_FLAGS_RELEASE        "${CMAKE_CXX_FLAGS_RELEASE}")
+    set(CMAKE_CXX_FLAGS_RELWITHDEBINFO "-g3 ${CMAKE_CXX_FLAGS_RELWITHDEBINFO}")
 elseif (MULTI_THREAD)
     set(CMAKE_CXX_FLAGS_DEBUG          "/MTd ${CMAKE_CXX_FLAGS_DEBUG}")
     set(CMAKE_CXX_FLAGS_MINSIZEREL     "/MT ${CMAKE_CXX_FLAGS_MINSIZEREL}")