diff --git a/metagpt/roles/role.py b/metagpt/roles/role.py
index ad3c44ac1..47a4f45a7 100644
--- a/metagpt/roles/role.py
+++ b/metagpt/roles/role.py
@@ -481,6 +481,8 @@ class Role(SerializationMixin, ContextMixin, BaseModel):
             rsp = await self._act_by_order()
         elif self.rc.react_mode == RoleReactMode.PLAN_AND_ACT:
             rsp = await self._plan_and_act()
+        else:
+            raise ValueError(f"Unsupported react mode: {self.rc.react_mode}")
         self._set_state(state=-1)  # current reaction is complete, reset state to -1 and todo back to None
         return rsp