diff --git a/haystack/nodes/other/join.py b/haystack/nodes/other/join.py
index 04b3f7b470..d2809648ef 100644
--- a/haystack/nodes/other/join.py
+++ b/haystack/nodes/other/join.py
@@ -22,7 +22,8 @@ def run(  # type: ignore
     ) -> Tuple[Dict, str]:
         if inputs:
             results = self.run_accumulated(inputs, top_k_join=top_k_join)
-            results[0]["root_node"] = inputs[0]["root_node"]
+            if "root_node" in inputs[0]:
+                results[0]["root_node"] = inputs[0]["root_node"]
             return results
         warnings.warn("You are using a JoinNode with only one input. This is usually equivalent to a no-op.")
         return self.run_accumulated(
@@ -58,7 +59,8 @@ def run_batch(  # type: ignore
     ) -> Tuple[Dict, str]:
         if inputs:
             results = self.run_batch_accumulated(inputs=inputs, top_k_join=top_k_join)
-            results[0]["root_node"] = inputs[0]["root_node"]
+            if "root_node" in inputs[0]:
+                results[0]["root_node"] = inputs[0]["root_node"]
             return results
         warnings.warn("You are using a JoinNode with only one input. This is usually equivalent to a no-op.")
         return self.run_batch_accumulated(