diff --git a/cmd/dex/config.go b/cmd/dex/config.go
index 3f51d95e..8f78eea2 100644
--- a/cmd/dex/config.go
+++ b/cmd/dex/config.go
@@ -25,7 +25,7 @@ import (
 )
 
 func configUnmarshaller(b []byte, v interface{}) error {
-	if featureflags.ConfigDisallowUnknownFields.Enabled() {
+	if !featureflags.ConfigDisallowUnknownFields.Enabled() {
 		return json.Unmarshal(b, v)
 	}
 	dec := json.NewDecoder(bytes.NewReader(b))