diff --git a/Formula/graph-tool.rb b/Formula/graph-tool.rb
index 0323c9399191..f43095330cdd 100644
--- a/Formula/graph-tool.rb
+++ b/Formula/graph-tool.rb
@@ -79,7 +79,10 @@ class GraphTool < Formula
 
   def install
     # Work around "error: no member named 'signbit' in the global namespace"
-    ENV["SDKROOT"] = MacOS.sdk_path if MacOS.version == :high_sierra
+    if MacOS.version == :high_sierra
+      ENV.delete "SDKROOT"
+      ENV.delete "HOMEBREW_SDKROOT"
+    end
 
     xy = Language::Python.major_minor_version "python3"
     venv = virtualenv_create(libexec, "python3")