diff --git a/src/Composer/Util/Platform.php b/src/Composer/Util/Platform.php
index 0028981b0..aeddce5e6 100644
--- a/src/Composer/Util/Platform.php
+++ b/src/Composer/Util/Platform.php
@@ -98,7 +98,7 @@ class Platform
 
         // detect msysgit/mingw and assume this is a tty because detection
         // does not work correctly, see https://github.com/composer/composer/issues/9690
-        if (in_array(strtoupper(getenv('MSYSTEM')), array('MINGW32', 'MINGW64'), true)) {
+        if (in_array(strtoupper(getenv('MSYSTEM') ?: ''), array('MINGW32', 'MINGW64'), true)) {
             return true;
         }