diff --git a/src/backends/gr.jl b/src/backends/gr.jl
index 989a0751..8ab730f3 100644
--- a/src/backends/gr.jl
+++ b/src/backends/gr.jl
@@ -853,7 +853,7 @@ function gr_display(sp::Subplot{GRBackend}, w, h, viewport_canvas)
             # create the colorbar of contour levels
             if sp[:colorbar] != :none
                 gr_set_viewport_cmap(sp)
-                l = round(Int32, 1000 + (h - ignorenan_minimum(h)) / (ignorenan_maximum(h) - ignorenan_minimum(h)) * 255)
+                l = round.(Int32, 1000 + (h - ignorenan_minimum(h)) / (ignorenan_maximum(h) - ignorenan_minimum(h)) * 255)
                 GR.setwindow(xmin, xmax, zmin, zmax)
                 GR.cellarray(xmin, xmax, zmax, zmin, 1, length(l), l)
                 ztick = 0.5 * GR.tick(zmin, zmax)