diff --git a/src/claude_agent_sdk/_internal/message_parser.py b/src/claude_agent_sdk/_internal/message_parser.py
index 931cc2a63..d1e18d8d4 100644
--- a/src/claude_agent_sdk/_internal/message_parser.py
+++ b/src/claude_agent_sdk/_internal/message_parser.py
@@ -95,6 +95,12 @@ def parse_message(data: dict[str, Any]) -> Message | None:
     match message_type:
         case "user":
             try:
+                if not isinstance(data["message"], dict):
+                    raise MessageParseError(
+                        f"Invalid message field (expected dict, got "
+                        f"{type(data['message']).__name__})",
+                        data,
+                    )
                 parent_tool_use_id = data.get("parent_tool_use_id")
                 tool_use_result = data.get("tool_use_result")
                 uuid = data.get("uuid")
@@ -150,6 +156,12 @@ def parse_message(data: dict[str, Any]) -> Message | None:
 
         case "assistant":
             try:
+                if not isinstance(data["message"], dict):
+                    raise MessageParseError(
+                        f"Invalid message field (expected dict, got "
+                        f"{type(data['message']).__name__})",
+                        data,
+                    )
                 raw_content = data["message"]["content"]
                 if not isinstance(raw_content, list):
                     raise MessageParseError(
diff --git a/tests/test_message_parser.py b/tests/test_message_parser.py
index e55fd1556..9ee093326 100644
--- a/tests/test_message_parser.py
+++ b/tests/test_message_parser.py
@@ -1015,6 +1015,15 @@ def test_non_dict_content_block_raises_documented_error(self, role: str) -> None
         with pytest.raises(MessageParseError):
             parse_message({"type": role, "message": message})
 
+    @pytest.mark.parametrize("role", ["assistant", "user"])
+    @pytest.mark.parametrize("bad_message", ["hi", ["hi"], 5, None])
+    def test_non_dict_message_field_raises_documented_error(
+        self, role: str, bad_message: object
+    ) -> None:
+        """A non-dict message field raises MessageParseError, never a raw TypeError."""
+        with pytest.raises(MessageParseError):
+            parse_message({"type": role, "message": bad_message})
+
     def test_parse_system_message_missing_fields(self):
         """Test that system message with missing fields raises MessageParseError."""
         with pytest.raises(MessageParseError) as exc_info: