diff --git a/fsl/fslview/slicecanvas.py b/fsl/fslview/slicecanvas.py
index 2b1a55b168472f085d364595636af3d01123df2b..c7d4cd8bf9b2a462b277f93a139da6bcb3cbc358 100644
--- a/fsl/fslview/slicecanvas.py
+++ b/fsl/fslview/slicecanvas.py
@@ -96,7 +96,7 @@ class SliceCanvas(wxgl.GLCanvas, props.HasProperties):
         """
 
         realHeight   = self.displayBounds.ylen
-        canvasHeight = float(self.GetClientSize().GetWidth())
+        canvasHeight = float(self.GetClientSize().GetHeight())
 
         if realHeight   == 0: return 0
         if canvasHeight == 0: return 0