diff --git a/haystack/nodes/prompt/prompt_node.py b/haystack/nodes/prompt/prompt_node.py
index c4a40e9b8a..d5186519fa 100644
--- a/haystack/nodes/prompt/prompt_node.py
+++ b/haystack/nodes/prompt/prompt_node.py
@@ -247,7 +247,10 @@ def _prepare(  # type: ignore
         """
         Prepare prompt invocation.
         """
-        invocation_context = invocation_context.copy() or {}
+        if invocation_context is None:
+            invocation_context = {}
+        else:
+            invocation_context = invocation_context.copy()
 
         if query and "query" not in invocation_context:
             invocation_context["query"] = query