diff --git a/mrDiffusion/roi/dtiRoiToImg.m b/mrDiffusion/roi/dtiRoiToImg.m
index 7919b7e0..419357b4 100644
--- a/mrDiffusion/roi/dtiRoiToImg.m
+++ b/mrDiffusion/roi/dtiRoiToImg.m
@@ -33,7 +33,7 @@
 end
 
 sz = diff(ceil(mrAnatXformCoords(inv(imgXform), bb)))+1;
-roiImg = false(sz);
+roiImg = false(abs(sz));
 % Remove coords outside the bounding box
 badCoords = coords(:,1)<bb(1,1) | coords(:,1)>bb(2,1) ...
           | coords(:,2)<bb(1,2) | coords(:,2)>bb(2,2) ...