diff --git a/keras_contrib/layers/crf.py b/keras_contrib/layers/crf.py
index 88a64ac69..3d43537d4 100644
--- a/keras_contrib/layers/crf.py
+++ b/keras_contrib/layers/crf.py
@@ -513,6 +513,7 @@ def recursion(self, input_energy, mask=None, go_backwards=False,
         constants = [chain_energy]
 
         if mask is not None:
+            mask = K.cast(mask, K.floatx())
             mask2 = K.cast(K.concatenate([mask, K.zeros_like(mask[:, :1])], axis=1),
                            K.floatx())
             constants.append(mask2)