diff --git a/schema/workflow.yaml b/schema/workflow.yaml
index 892aa0d5..66d89ce6 100644
--- a/schema/workflow.yaml
+++ b/schema/workflow.yaml
@@ -1148,11 +1148,11 @@ $defs:
       - title: LiteralUriTemplate
         type: string
         format: uri-template
-        pattern: "^http(s?)://.*"
+        pattern: "^[A-Za-z][A-Za-z0-9+\\-.]*://.*"
       - title: LiteralUri
         type: string
         format: uri
-        pattern: "^http(s?)://.*"
+        pattern: "^[A-Za-z][A-Za-z0-9+\\-.]*://.*"
   endpoint:
     title: Endpoint
     description: Represents an endpoint.