diff --git a/src/claude_agent_sdk/_internal/message_parser.py b/src/claude_agent_sdk/_internal/message_parser.py
index 931cc2a63..160bd745e 100644
--- a/src/claude_agent_sdk/_internal/message_parser.py
+++ b/src/claude_agent_sdk/_internal/message_parser.py
@@ -147,6 +147,11 @@ def parse_message(data: dict[str, Any]) -> Message | None:
                 raise MessageParseError(
                     f"Missing required field in user message: {e}", data
                 ) from e
+            except (TypeError, AttributeError) as e:
+                # e.g. data["message"] is not a dict, so indexing into it fails
+                raise MessageParseError(
+                    f"Malformed user message: {e}", data
+                ) from e
 
         case "assistant":
             try:
@@ -222,6 +227,11 @@ def parse_message(data: dict[str, Any]) -> Message | None:
                 raise MessageParseError(
                     f"Missing required field in assistant message: {e}", data
                 ) from e
+            except (TypeError, AttributeError) as e:
+                # e.g. data["message"] is not a dict, so indexing into it fails
+                raise MessageParseError(
+                    f"Malformed assistant message: {e}", data
+                ) from e
 
         case "system":
             try:
diff --git a/tests/test_message_parser.py b/tests/test_message_parser.py
index e55fd1556..0962d3c6e 100644
--- a/tests/test_message_parser.py
+++ b/tests/test_message_parser.py
@@ -976,6 +976,13 @@ def test_parse_invalid_data_type(self):
         assert "Invalid message data type" in str(exc_info.value)
         assert "expected dict, got str" in str(exc_info.value)
 
+    def test_parse_non_dict_message_field(self):
+        """A non-dict 'message' field raises MessageParseError, not a bare TypeError."""
+        for message_type in ("user", "assistant"):
+            with pytest.raises(MessageParseError) as exc_info:
+                parse_message({"type": message_type, "message": "not a dict"})
+            assert f"Malformed {message_type} message" in str(exc_info.value)
+
     def test_parse_missing_type_field(self):
         """Test that missing 'type' field raises MessageParseError."""
         with pytest.raises(MessageParseError) as exc_info: