https://bugs.gentoo.org/867424
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -146,13 +146,13 @@ if(CMAKE_CXX_COMPILER_ID STREQUAL "GNU"
     OR CMAKE_CXX_COMPILER_ID STREQUAL "Clang")
   # XXX figure out how to get "-std=c++14 -fno-rtti" from LLVM.  That's how we
   # get those options in the Automake path...
-  set(CMAKE_C_FLAGS "${CMAKE_C_FLAGS} -Wall -Wextra -Werror -Wno-error=maybe-uninitialized")
-  set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -std=c++14 -fno-rtti -fno-strict-aliasing -Wall -Wextra -Wno-unused-parameter -Werror -Wno-error=maybe-uninitialized")
+  set(CMAKE_C_FLAGS "${CMAKE_C_FLAGS} -Wall -Wextra -Wno-error=maybe-uninitialized")
+  set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -std=c++14 -fno-rtti -fno-strict-aliasing -Wall -Wextra -Wno-unused-parameter -Wno-error=maybe-uninitialized")
   if(SUPPORTS_FVISIBILITY_INLINES_HIDDEN_FLAG)
     set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -fvisibility-inlines-hidden")
   endif()
-  set(CMAKE_CXX_FLAGS_RELEASE "${CMAKE_CXX_FLAGS_RELEASE} -O3")
-  set(CMAKE_CXX_FLAGS_RELWITHDEBINFO "${CMAKE_CXX_FLAGS_RELEASE} -O3")
+  set(CMAKE_CXX_FLAGS_RELEASE "${CMAKE_CXX_FLAGS_RELEASE}")
+  set(CMAKE_CXX_FLAGS_RELWITHDEBINFO "${CMAKE_CXX_FLAGS_RELEASE}")
 endif()
 
 ###############################################################################
diff --git a/CMakeLists.txt b/CMakeLists.txt
index 261a0fb..cbaebc3 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -151,8 +151,6 @@ if(CMAKE_CXX_COMPILER_ID STREQUAL "GNU"
   if(SUPPORTS_FVISIBILITY_INLINES_HIDDEN_FLAG)
     set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -fvisibility-inlines-hidden")
   endif()
-  set(CMAKE_CXX_FLAGS_RELEASE "${CMAKE_CXX_FLAGS_RELEASE}")
-  set(CMAKE_CXX_FLAGS_RELWITHDEBINFO "${CMAKE_CXX_FLAGS_RELEASE}")
 endif()
 
 ###############################################################################