diff --git a/appveyor.yml b/appveyor.yml
index da703786..828c3223 100644
--- a/appveyor.yml
+++ b/appveyor.yml
@@ -6,8 +6,8 @@ os:
 
 environment:
   matrix:
-  - additional_flags: ""
-  - additional_flags: "/permissive- /std:c++latest /utf-8"
+  - additional_flags: "/Wall"
+  - additional_flags: "/permissive- /std:c++latest /utf-8 /Wall"
 
 matrix:
   exclude: