diff --git a/aider/sendchat.py b/aider/sendchat.py
index 59f67c53e..379ec62d7 100644
--- a/aider/sendchat.py
+++ b/aider/sendchat.py
@@ -19,16 +19,24 @@ RETRY_TIMEOUT = 60
 def sanity_check_messages(messages):
     """Check if messages alternate between user and assistant roles.
     System messages can be interspersed anywhere.
+    Also verifies the last non-system message is from the user.
     Returns True if valid, False otherwise."""
     last_role = None
+    last_non_system_role = None
+    
     for msg in messages:
         role = msg.get("role")
         if role == "system":
             continue
+            
         if last_role and role == last_role:
             return False
+            
         last_role = role
-    return True
+        last_non_system_role = role
+        
+    # Ensure last non-system message is from user
+    return last_non_system_role == "user"
 
 
 def send_completion(