diff --git a/robosat/fpn.py b/robosat/fpn.py
index 8b3f0b49..5a323a7d 100644
--- a/robosat/fpn.py
+++ b/robosat/fpn.py
@@ -46,6 +46,9 @@ def __init__(self, num_filters=256, pretrained=True):
     def forward(self, x):
         # Bottom-up pathway, from ResNet
 
+        size = x.size()
+        assert size[-1] % 32 == 0 and size[-2] % 32 == 0, "image resolution has to be divisible by 32 for resnet"
+
         enc0 = self.resnet.conv1(x)
         enc0 = self.resnet.bn1(enc0)
         enc0 = self.resnet.relu(enc0)