diff --git a/CMakeLists.txt b/CMakeLists.txt
index 4411285..390325d 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -69,7 +69,7 @@ if (${IS_GNU})
     if (CMAKE_CXX_COMPILER_VERSION VERSION_LESS ${MINIMAL_GNU})
         message(FATAL_ERROR "G++ ${MINIMAL_GNU} or higher is required.")
     endif()
-    set(CMAKE_CXX_FLAGS_RELEASE "${CMAKE_CXX_FLAGS_RELEASE} -foptimize-strlen -fsched-pressure -flive-range-shrinkage -fpredictive-commoning -ftree-partial-pre -fira-loop-pressure -ftree-loop-distribution -floop-interchange -fsplit-paths -fgcse-las -fgcse-sm -fipa-pta -fstdarg-opt -fivopts -s")
+    set(CMAKE_CXX_FLAGS_RELEASE "${CMAKE_CXX_FLAGS_RELEASE} -foptimize-strlen -fsched-pressure -flive-range-shrinkage -fpredictive-commoning -ftree-partial-pre -ftree-parallelize-loops=2 -fira-loop-pressure -ftree-loop-distribution -floop-interchange -fsplit-paths -fgcse-las -fgcse-sm -fipa-pta -fstdarg-opt -fivopts -s")
     set(CMAKE_CXX_FLAGS "-fno-use-linker-plugin -fwhole-program ${CMAKE_CXX_FLAGS}")
 elseif(${IS_CLANG})
     if (CMAKE_CXX_COMPILER_VERSION VERSION_LESS ${MINIMAL_CLANG})