diff --git a/src/Gnuplot.jl b/src/Gnuplot.jl
index f3d9b4a..dbedc21 100644
--- a/src/Gnuplot.jl
+++ b/src/Gnuplot.jl
@@ -1570,7 +1570,7 @@ mutable struct IsoContourLines
         @assert length(z) == 1
         data = Vector{String}()
         for i in 1:length(paths)
-            append!(data, arrays2datablock(paths[i].x, paths[i].y))
+            append!(data, arrays2datablock(paths[i].x, paths[i].y, z .* fill(1., length(paths[i].x)))
             push!(data, "")
         end
         return new(paths, data, z)