diff --git a/appveyor.yml b/appveyor.yml
index 409f5230..f1122d59 100644
--- a/appveyor.yml
+++ b/appveyor.yml
@@ -10,8 +10,8 @@ os:
 
 environment:
   matrix:
-  - additional_flags: "${CMAKE_CXXFLAGS}"
-  - additional_flags: "${CMAKE_CXXFLAGS} /permissive- /std:c++latest /utf-8"
+  - additional_flags: ""
+  - additional_flags: "/permissive- /std:c++latest /utf-8"
 
 init: []
 
@@ -19,7 +19,7 @@ install: []
 
 build_script:
   - IF "%APPVEYOR_BUILD_WORKER_IMAGE%" == "Visual Studio 2015" ( SET GEN="Visual Studio 14 2015") ELSE (SET GEN="Visual Studio 15 2017")
-  - cmake . -G%GEN% -DCMAKE_CXX_FLAGS=%additional_flags%
+  - cmake . -G%GEN% -DCMAKE_CXX_FLAGS="${CMAKE_CXXFLAGS} %additional_flags%"
   - cmake --build . --config Release
 
 test_script: