diff --git a/biomes/model.py b/biomes/model.py
index 8ef0ae7..12dd1b3 100644
--- a/biomes/model.py
+++ b/biomes/model.py
@@ -121,7 +121,7 @@ class Model():
         # map_callback = MapHistory()
 
         extra_params = {}
-        if self.class_weight:
+        if self.class_weight.any():
             extra_params['class_weight'] = self.class_weight
 
         out = self.model.fit(