diff --git a/src/backends/gr.jl b/src/backends/gr.jl
index f35866c9..cf369f64 100644
--- a/src/backends/gr.jl
+++ b/src/backends/gr.jl
@@ -144,6 +144,7 @@ gr_set_fillcolor(c)   = GR.setfillcolorind(gr_getcolorind(_cycle(c,1)))
 gr_set_markercolor(c) = GR.setmarkercolorind(gr_getcolorind(_cycle(c,1)))
 gr_set_textcolor(c)   = GR.settextcolorind(gr_getcolorind(_cycle(c,1)))
 gr_set_transparency(α::Real) = GR.settransparency(clamp(α, 0, 1))
+function gr_set_transparency(::Void) end
 
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