diff --git a/CHANGELOG.md b/CHANGELOG.md
index d08d9d76a..d7fd8655f 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -14,7 +14,6 @@
 - Human Agent: Don't emit sandbox events for human agent
 - Inspect View: Improve rendering of JSON within logging events.
 - Inspect View: Improve virtualized rendering of Sample List, Sample Transcript, and Sample Messages.
-- Bugfix: Catch standard `TimeoutError` for running shell commands in the computer tool container.
 - Inspect View: Fix layout issues with human agent terminal session playback.
 - Inspect View: Improve tool input / output appearance when rendered in VSCode.
 - Inspect View: Display reasoning tokens in model usage for the samples and for the complete eval.
@@ -22,6 +21,8 @@
 - Inspect View: Improve rendering of some tool calls in the transcript.
 - Bugfix: Fix audio and video inputs for new Google GenAI client.
 - Bugfix: Ensure that token limits are not enforced during model graded scoring.
+- Bugfix: Catch standard `TimeoutError` for running shell commands in the computer tool container.
+- Bugfix: Correct combination of consecutive string based user messages for Anthropic provider.
 
 ## v0.3.70 (25 February 2025)
 
diff --git a/src/inspect_ai/model/_providers/anthropic.py b/src/inspect_ai/model/_providers/anthropic.py
index c2b9f441f..00879e84c 100644
--- a/src/inspect_ai/model/_providers/anthropic.py
+++ b/src/inspect_ai/model/_providers/anthropic.py
@@ -562,7 +562,7 @@ def combine_messages(a: MessageParam, b: MessageParam) -> MessageParam:
     role = a["role"]
     a_content = a["content"]
     b_content = b["content"]
-    if isinstance(a_content, str) and isinstance(a_content, str):
+    if isinstance(a_content, str) and isinstance(b_content, str):
         return MessageParam(role=role, content=f"{a_content}\n{b_content}")
     elif isinstance(a_content, list) and isinstance(b_content, list):
         return MessageParam(role=role, content=a_content + b_content)