diff --git a/utils/torch_utils.py b/utils/torch_utils.py
index aa42cb0f..ef87d6ca 100644
--- a/utils/torch_utils.py
+++ b/utils/torch_utils.py
@@ -14,10 +14,11 @@ def init_seeds(seed=0):
         torch.backends.cudnn.benchmark = False
 
 
-def select_device(device=None, apex=False):
-    if device == 'cpu':
+def select_device(device='', apex=False):
+    if device.lower() == 'cpu':
         pass
     elif device:  # Set environment variable if device is specified
+        assert torch.cuda.is_available(), 'CUDA unavailable, invalid device %s requested' % device
         os.environ['CUDA_VISIBLE_DEVICES'] = device
 
     # apex if mixed precision training https://github.com/NVIDIA/apex