diff --git a/CMakeLists.txt b/CMakeLists.txt
index d9c18554fd..8c76739308 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -42,8 +42,8 @@ if (STATIC_BUILD)
     if(${CMAKE_SYSTEM_NAME} MATCHES "Darwin")
     elseif(${CMAKE_SYSTEM_NAME} MATCHES "Windows")
         if (MSVC)
-            set(CMAKE_CXX_FLAGS_RELEASE "/MT")
-            set(CMAKE_CXX_FLAGS_DEBUG "/MTd")
+            set(CMAKE_CXX_FLAGS_RELEASE "${CMAKE_CXX_FLAGS_RELEASE} /MT")
+            set(CMAKE_CXX_FLAGS_DEBUG "${CMAKE_CXX_FLAGS_DEBUG} /MTd")
         endif()
     else()
         set(CMAKE_FIND_LIBRARY_SUFFIXES ".a" ".so")
@@ -97,11 +97,11 @@ if (MSVC)
     set(CMAKE_CXX_FLAGS_DEBUG "${CMAKE_CXX_FLAGS_DEBUG} /D_DEBUG /W4 /wd4100 /wd4244 /wd4125 /wd4800 /wd4456 /wd4458 /wd4305 /wd4459 /wd4121 /wd4996")
     set(CMAKE_CXX_FLAGS_RELEASE "${CMAKE_CXX_FLAGS_RELEASE} /W4 /wd4100 /wd4244 /wd4125 /wd4800 /wd4456 /wd4458 /wd4305 /wd4459 /wd4121 /wd4996 /wd4127")
 else()
-    set(CMAKE_CXX_FLAGS_DEBUG "-Wall -fPIC -ggdb -pipe")
+    set(CMAKE_CXX_FLAGS_DEBUG "${CMAKE_CXX_FLAGS_DEBUG} -Wall -fPIC -ggdb -pipe")
     if (USE_OPENMP)
-        set(CMAKE_CXX_FLAGS_RELEASE "-Wall -fPIC -O3 -g -pipe -fopenmp")
+        set(CMAKE_CXX_FLAGS_RELEASE "${CMAKE_CXX_FLAGS_RELEASE} -Wall -fPIC -O3 -g -pipe -fopenmp")
     else()
-        set(CMAKE_CXX_FLAGS_RELEASE "-Wall -fPIC -O3 -g -pipe")
+        set(CMAKE_CXX_FLAGS_RELEASE "${CMAKE_CXX_FLAGS_RELEASE} -Wall -fPIC -O3 -g -pipe")
     endif()
 endif()