diff --git a/docs/make.jl b/docs/make.jl
index f6a05e4..d6336e3 100644
--- a/docs/make.jl
+++ b/docs/make.jl
@@ -1,6 +1,10 @@
 using IntervalSets
 using Documenter
 
+# We need to set `ENV["GKSwstype"]` to suppress the warning on GitHub Actions.
+# https://github.com/JuliaPlots/Plots.jl/issues/1076#issuecomment-327509819
+ENV["GKSwstype"] = "100"
+
 DocMeta.setdocmeta!(IntervalSets, :DocTestSetup, :(using IntervalSets); recursive=true)
 
 makedocs(;