diff --git a/CI/before_script.msvc.sh b/CI/before_script.msvc.sh
index 72c3e983a..04f89ccd4 100644
--- a/CI/before_script.msvc.sh
+++ b/CI/before_script.msvc.sh
@@ -2,8 +2,8 @@
 
 set -euo pipefail
 
-APPVEYOR=""
-CI=""
+APPVEYOR=${APPVEYOR:-}
+CI=${CI:-}
 
 VERBOSE=""
 STRIP=""