diff --git a/build/tools/travis-ci.sh b/build/tools/travis-ci.sh
index bc5a52abee..ab8563d5df 100755
--- a/build/tools/travis-ci.sh
+++ b/build/tools/travis-ci.sh
@@ -16,15 +16,23 @@ launch_httpbin() {
     echo 'travis_fold:start:httpbin'
     echo 'Running httpbin...'
 
+    case "$(uname -s)" in
+        Linux)
+            dist_codename=$(lsb_release --codename --short)
+            ;;
+    esac
+
     # We need to disable SSL certificate checking under Trusty because Python
     # version there is too old to support SNI.
-    case "$(lsb_release --codename --short)" in
+    case "$dist_codename" in
         trusty)
             pip_args='--trusted-host files.pythonhosted.org'
             ;;
     esac
 
-    pip install httpbin --user $pip_args
+    # decorator 5+ is incompatible with Python 2 which we still use under in
+    # some builds, so explicitly select version 4.4 which is known to work.
+    pip install decorator==4.4.2 httpbin --user $pip_args
     python -m httpbin.core &
     WX_TEST_WEBREQUEST_URL="http://localhost:5000"