diff --git a/src/backends/plotly.jl b/src/backends/plotly.jl
index 30d0c05c..64c9f21d 100644
--- a/src/backends/plotly.jl
+++ b/src/backends/plotly.jl
@@ -922,15 +922,6 @@ end
 # ----------------------------------------------------------------
 
 
-function _show(io::IO, ::MIME"image/png", plt::Plot{PlotlyBackend})
-    # show_png_from_html(io, plt)
-    error("png output from the plotly backend is not supported.  Please use plotlyjs instead.")
-end
-
-function _show(io::IO, ::MIME"image/svg+xml", plt::Plot{PlotlyBackend})
-    error("svg output from the plotly backend is not supported.  Please use plotlyjs instead.")
-end
-
 function Base.show(io::IO, ::MIME"text/html", plt::Plot{PlotlyBackend})
     prepare_output(plt)
     write(io, html_head(plt) * html_body(plt))
diff --git a/src/output.jl b/src/output.jl
index 6344ba9c..e4b7e657 100644
--- a/src/output.jl
+++ b/src/output.jl
@@ -195,10 +195,11 @@ function Base.show(io::IO, ::MIME"text/html", plt::Plot)
     end
 end
 
-function _show(io::IO, m, plt::Plot{B}) where B
-    # Base.show_backtrace(STDOUT, backtrace())
-    warn("_show is not defined for this backend. m=", string(m))
+# delegate mimewritable (showable on julia 0.7) to _show instead
+function Base.mimewritable(m::M, plt::P) where {M<:MIME, P<:Plot}
+    return method_exists(_show, Tuple{IO, M, P})
 end
+
 function _display(plt::Plot)
     warn("_display is not defined for this backend.")
 end