diff --git a/etc/taskcluster/decision_task.py b/etc/taskcluster/decision_task.py
index fe5931ff07d..3bce2b298d1 100644
--- a/etc/taskcluster/decision_task.py
+++ b/etc/taskcluster/decision_task.py
@@ -489,6 +489,7 @@ def update_wpt():
         .with_repo()
         .with_curl_artifact_script(build_task, "target.tar.gz")
         .with_script("""
+            export PKG_CONFIG_PATH="$(brew --prefix libffi)/lib/pkgconfig/"
             tar -xzf target.tar.gz
             ./etc/ci/update-wpt-checkout fetch-and-update-expectations
             ./etc/ci/update-wpt-checkout open-pr