diff --git a/CMakeLists.txt b/CMakeLists.txt
index d780315d8939bee82fdb79fb09ecff9e4178d608..15bd60549caca7313d1bb9f18e831077ab2e6752 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -38,8 +38,8 @@ endif()
 
 # enable warnings and disallow non-standard language
 set(CMAKE_CXX_FLAGS "-Wall -pedantic -Wextra -Wno-ignored-qualifiers")
-set(CMAKE_CXX_FLAGS_DEBUG "${CMAKE_CXX_FLAGS} -O0 -g")
-set(CMAKE_CXX_FLAGS_RELEASE "${CMAKE_CXX_FLAGS} -O3")
+set(CMAKE_CXX_FLAGS_DEBUG "-O0 -g")
+set(CMAKE_CXX_FLAGS_RELEASE "-O3")
 
 # clang produces a lot of unecessary warnings without this:
 add_compile_options("$<$<CXX_COMPILER_ID:Clang>:-Wno-nonportable-include-path>")