diff --git a/fsl/data/atlases.py b/fsl/data/atlases.py
index a17ca031b429e21ef17a74c515db6ba128e5ff8d..5982473edb2dcf3d7b4e0faed680fef56d725abf 100644
--- a/fsl/data/atlases.py
+++ b/fsl/data/atlases.py
@@ -406,7 +406,7 @@ class ProbabilisticAtlas(Atlas):
                   location is out of bounds.
         """
         voxelLoc = transform.transform([worldLoc], self.worldToVoxMat.T)[0]
-        voxelLoc = voxelLoc.round()
+        voxelLoc = [int(v) for v in voxelLoc.round()]
 
         if voxelLoc[0] <  0             or \
            voxelLoc[1] <  0             or \