diff --git a/libs/langchain/langchain/memory/combined.py b/libs/langchain/langchain/memory/combined.py
index 1c46c184d4..80316755ae 100644
--- a/libs/langchain/langchain/memory/combined.py
+++ b/libs/langchain/langchain/memory/combined.py
@@ -61,10 +61,12 @@ class CombinedMemory(BaseMemory):
         # Collect vars from all sub-memories
         for memory in self.memories:
             data = memory.load_memory_variables(inputs)
-            memory_data = {
-                **memory_data,
-                **data,
-            }
+            for key, value in data.items():
+                if key in memory_data:
+                    raise ValueError(
+                        f"The variable {key} is repeated in the CombinedMemory."
+                    )
+                memory_data[key] = value
 
         return memory_data