diff --git a/include/exec/user/thunk.h b/include/exec/user/thunk.h
index 8f55b233b39c95659d4a7f7ed6febb31b5244d25..8d3af5a3be9d8150fb0a88814233f2393b124d63 100644
--- a/include/exec/user/thunk.h
+++ b/include/exec/user/thunk.h
@@ -135,7 +135,7 @@ static inline int thunk_type_size(const argtype *type_ptr, int is_host)
         se = struct_entries + type_ptr[1];
         return se->size[is_host];
     default:
-        return -1;
+        g_assert_not_reached();
     }
 }
 
@@ -185,7 +185,7 @@ static inline int thunk_type_align(const argtype *type_ptr, int is_host)
         se = struct_entries + type_ptr[1];
         return se->align[is_host];
     default:
-        return -1;
+        g_assert_not_reached();
     }
 }