diff --git a/pkg/scalers/gcp_pub_sub_scaler.go b/pkg/scalers/gcp_pub_sub_scaler.go
index d14133ef3e6..dcd0be31e15 100644
--- a/pkg/scalers/gcp_pub_sub_scaler.go
+++ b/pkg/scalers/gcp_pub_sub_scaler.go
@@ -21,7 +21,7 @@ import (
 const (
 	defaultTargetSubscriptionSize = 5
 	pubSubStackDriverMetricName   = "pubsub.googleapis.com/subscription/num_undelivered_messages"
-	compositeSubscriptionIDPrefix = "projects/[a-zA-Z0-9-]+/subscriptions/[a-zA-Z0-9-]+"
+	compositeSubscriptionIDPrefix = "projects/[a-z][a-zA-Z0-9-]*[a-zA-Z0-9]/subscriptions/[a-zA-Z][a-zA-Z0-9-_~%+]*"
 )
 
 type gcpAuthorizationMetadata struct {