diff --git a/src/Mod/Assembly/UtilsAssembly.py b/src/Mod/Assembly/UtilsAssembly.py
index 3e88d7dd2c..ca26472864 100644
--- a/src/Mod/Assembly/UtilsAssembly.py
+++ b/src/Mod/Assembly/UtilsAssembly.py
@@ -1140,6 +1140,8 @@ def isRefValid(ref, number_sub):
         return False
     if len(ref[1]) < number_sub:
         return False
+    if ref[1][0].find("?") != -1:
+        return False
 
     return True