diff --git a/aider/coder.py b/aider/coder.py
index f11433753..76544fdc8 100755
--- a/aider/coder.py
+++ b/aider/coder.py
@@ -298,7 +298,10 @@ class Coder:
             dict(role="user", content=inp),
         ]
 
-        main_sys = self.gpt_prompts.main_system + "\n" + self.gpt_prompts.system_reminder
+        main_sys = self.gpt_prompts.main_system
+        if self.main_model == "gpt-4":
+            main_sys += "\n" + self.gpt_prompts.system_reminder
+
         messages = [
             dict(role="system", content=main_sys),
         ]
diff --git a/aider/commands.py b/aider/commands.py
index 56906e4e6..8340a2d90 100644
--- a/aider/commands.py
+++ b/aider/commands.py
@@ -118,7 +118,8 @@ class Commands:
             "was reset and removed from git.\n"
         )
 
-        return prompts.undo_command_reply
+        if self.coder.main_model != "gpt-3.5-turbo":
+            return prompts.undo_command_reply
 
     def cmd_diff(self, args):
         "Display the diff of the last aider commit"
diff --git a/aider/prompts.py b/aider/prompts.py
index 26e6c9be6..3cff17937 100644
--- a/aider/prompts.py
+++ b/aider/prompts.py
@@ -70,7 +70,7 @@ If the request is ambiguous, ask questions.
 
 Once you understand the request you MUST:
 1. Think step-by-step and *briefly* explain the needed code changes.
-2. Output a new copy of each file which needs code changes.
+2. If changes are needed, output a copy of each file that needs changes.
 """
 
     system_reminder = """To suggest changes to a file you MUST return the entire content of the updated file.
@@ -84,6 +84,7 @@ exact/path/to/filename.js
 """
 
     files_content_prefix = "Here is the current content of the files:\n"
+    files_no_full_files = "I am not sharing any files yet."
 
 
 # COMMIT