diff --git a/src/dawg.pyx b/src/dawg.pyx
index 133c7fc..eb20c9f 100644
--- a/src/dawg.pyx
+++ b/src/dawg.pyx
@@ -86,7 +86,7 @@ cdef class DAWG:
     cpdef bint b_has_key(self, bytes key) except -1:
         return self.dct.Contains(key, len(key))
 
-    cpdef bytes tobytes(self):
+    cpdef bytes tobytes(self) except +:
         """
         Return raw DAWG content as bytes.
         """
diff --git a/update_cpp.sh b/update_cpp.sh
index 86dcf94..7f771a7 100755
--- a/update_cpp.sh
+++ b/update_cpp.sh
@@ -1,2 +1,2 @@
 #!/bin/sh
-cython src/*.pyx src/*.pxd -a --cplus
+cython src/*.pyx src/*.pxd -a --cplus -2