diff --git a/mhcflurry/class1_neural_network.py b/mhcflurry/class1_neural_network.py
index 583832015810e15f984dc7d76d683b55c0d5f8ff..6e1b3148c381b2b838c7cf9ce42b337ce3d03a08 100644
--- a/mhcflurry/class1_neural_network.py
+++ b/mhcflurry/class1_neural_network.py
@@ -585,7 +585,7 @@ class Class1NeuralNetwork(object):
                 initial_epoch=epoch - 1,
                 epochs=epoch,
                 use_multiprocessing=False,
-                workers=1,
+                workers=0,
                 validation_data=(validation_x_dict, validation_y_dict),
                 verbose=verbose,
             )