diff --git a/src/series.jl b/src/series.jl
index 31191fd2..12944a77 100644
--- a/src/series.jl
+++ b/src/series.jl
@@ -10,6 +10,9 @@ const FuncOrFuncs{F} = Union{F, Vector{F}, Matrix{F}}
 
 all3D(d::KW) = trueOrAllTrue(st -> st in (:contour, :contourf, :heatmap, :surface, :wireframe, :contour3d, :image), get(d, :seriestype, :none))
 
+# unknown
+convertToAnyVector(x, d::KW) = error("No user recipe defined for $(typeof(x))")
+
 # missing
 convertToAnyVector(v::Void, d::KW) = Any[nothing], nothing