diff --git a/cc/config/global.go b/cc/config/global.go
index bae5555f9..6b02429f4 100644
--- a/cc/config/global.go
+++ b/cc/config/global.go
@@ -165,6 +165,9 @@ func init() {
 			flags = append(flags, "-ftrivial-auto-var-init=zero -enable-trivial-auto-var-init-zero-knowing-it-will-be-removed-from-clang")
 		} else if ctx.Config().IsEnvTrue("AUTO_PATTERN_INITIALIZE") {
 			flags = append(flags, "-ftrivial-auto-var-init=pattern")
+		} else {
+			// Default to pattern initialization.
+			flags = append(flags, "-ftrivial-auto-var-init=pattern")
 		}
 
 		return strings.Join(flags, " ")