diff --git a/cmake/EthCompilerSettings.cmake b/cmake/EthCompilerSettings.cmake
index 8cf8b51b4..24252cc0b 100644
--- a/cmake/EthCompilerSettings.cmake
+++ b/cmake/EthCompilerSettings.cmake
@@ -6,7 +6,7 @@ if ("${CMAKE_CXX_COMPILER_ID}" MATCHES "GNU")
 	set(CMAKE_CXX_FLAGS "-std=c++11 -Wall -Wno-unknown-pragmas -Wextra -DSHAREDLIB -fPIC")
 	set(CMAKE_CXX_FLAGS_DEBUG          "-O0 -g -DETH_DEBUG")
 	set(CMAKE_CXX_FLAGS_MINSIZEREL     "-Os -DNDEBUG -DETH_RELEASE")
-	set(CMAKE_CXX_FLAGS_RELEASE        "-O4 -DNDEBUG -DETH_RELEASE")
+	set(CMAKE_CXX_FLAGS_RELEASE        "-O3 -DNDEBUG -DETH_RELEASE")
 	set(CMAKE_CXX_FLAGS_RELWITHDEBINFO "-O2 -g -DETH_DEBUG")
 	set(ETH_SHARED 1)
 
@@ -21,7 +21,7 @@ elseif ("${CMAKE_CXX_COMPILER_ID}" MATCHES "Clang")
 	set(CMAKE_CXX_FLAGS "-std=c++11 -Wall -Wno-unknown-pragmas -Wextra -DSHAREDLIB -fPIC")
 	set(CMAKE_CXX_FLAGS_DEBUG          "-O0 -g -DETH_DEBUG")
 	set(CMAKE_CXX_FLAGS_MINSIZEREL     "-Os -DNDEBUG -DETH_RELEASE")
-	set(CMAKE_CXX_FLAGS_RELEASE        "-O4 -DNDEBUG -DETH_RELEASE")
+	set(CMAKE_CXX_FLAGS_RELEASE        "-O3 -DNDEBUG -DETH_RELEASE")
 	set(CMAKE_CXX_FLAGS_RELWITHDEBINFO "-O2 -g -DETH_DEBUG")
 	set(ETH_SHARED 1)