diff --git a/s08_context_compact/README.en.md b/s08_context_compact/README.en.md
index dcf254cc..15199c37 100644
--- a/s08_context_compact/README.en.md
+++ b/s08_context_compact/README.en.md
@@ -46,10 +46,12 @@ def snip_compact(messages, max_messages=50):
     if len(messages) <= max_messages:
         return messages
     head_end, tail_start = 3, len(messages) - (max_messages - 3)
-    if _message_has_tool_use(messages[head_end - 1]):
+    if head_end > 0 and _message_has_tool_use(messages[head_end - 1]):
         while head_end < len(messages) and _is_tool_result_message(messages[head_end]):
             head_end += 1
-    if _is_tool_result_message(messages[tail_start]) and _message_has_tool_use(messages[tail_start - 1]):
+    if (tail_start > 0 and tail_start < len(messages)
+            and _is_tool_result_message(messages[tail_start])
+            and _message_has_tool_use(messages[tail_start - 1])):
         tail_start -= 1
     snipped = tail_start - head_end
     placeholder = {"role": "user", "content": f"[snipped {snipped} messages from conversation middle]"}
diff --git a/s08_context_compact/README.ja.md b/s08_context_compact/README.ja.md
index 72cae428..da174d0a 100644
--- a/s08_context_compact/README.ja.md
+++ b/s08_context_compact/README.ja.md
@@ -46,10 +46,12 @@ def snip_compact(messages, max_messages=50):
     if len(messages) <= max_messages:
         return messages
     head_end, tail_start = 3, len(messages) - (max_messages - 3)
-    if _message_has_tool_use(messages[head_end - 1]):
+    if head_end > 0 and _message_has_tool_use(messages[head_end - 1]):
         while head_end < len(messages) and _is_tool_result_message(messages[head_end]):
             head_end += 1
-    if _is_tool_result_message(messages[tail_start]) and _message_has_tool_use(messages[tail_start - 1]):
+    if (tail_start > 0 and tail_start < len(messages)
+            and _is_tool_result_message(messages[tail_start])
+            and _message_has_tool_use(messages[tail_start - 1])):
         tail_start -= 1
     snipped = tail_start - head_end
     placeholder = {"role": "user", "content": f"[snipped {snipped} messages from conversation middle]"}
diff --git a/s08_context_compact/README.md b/s08_context_compact/README.md
index 771257d4..ab5dae54 100644
--- a/s08_context_compact/README.md
+++ b/s08_context_compact/README.md
@@ -46,10 +46,12 @@ def snip_compact(messages, max_messages=50):
     if len(messages) <= max_messages:
         return messages
     head_end, tail_start = 3, len(messages) - (max_messages - 3)
-    if _message_has_tool_use(messages[head_end - 1]):
+    if head_end > 0 and _message_has_tool_use(messages[head_end - 1]):
         while head_end < len(messages) and _is_tool_result_message(messages[head_end]):
             head_end += 1
-    if _is_tool_result_message(messages[tail_start]) and _message_has_tool_use(messages[tail_start - 1]):
+    if (tail_start > 0 and tail_start < len(messages)
+            and _is_tool_result_message(messages[tail_start])
+            and _message_has_tool_use(messages[tail_start - 1])):
         tail_start -= 1
     snipped = tail_start - head_end
     placeholder = {"role": "user", "content": f"[snipped {snipped} messages from conversation middle]"}