diff --git a/lib/bb/parse/ast.py b/lib/bb/parse/ast.py
index e6ff1ff76..f9d93aa0f 100644
--- a/lib/bb/parse/ast.py
+++ b/lib/bb/parse/ast.py
@@ -373,7 +373,7 @@ class AddFragmentsNode(AstNode):
                         loginfo["detail"] = f"{value} ({self.fragments_variable} contains \"{fragment}\")"
                         break
                 # parsing=True since we want to emulate X=Y and allow X:override=Z to continue to exist
-                data.setVar(builtin_fragments[prefix], value, parsing=True, **loginfo)
+                data.setVarFlag(builtin_fragments[prefix], '_defaultval', value, parsing=True, **loginfo)
                 return True
             return False