diff --git a/css/build-css-testsuites.sh b/css/build-css-testsuites.sh
index cf40f562471753..3ec72652f31daf 100755
--- a/css/build-css-testsuites.sh
+++ b/css/build-css-testsuites.sh
@@ -35,6 +35,11 @@ main() {
             exit 1
         fi
 
+        if [ `$PYTHON -c 'import sys; print(sys.maxunicode)'` != "1114111" ]; then
+            echo "UCS-4 support for Python is required"
+            exit 1
+        fi
+
         virtualenv -p $PYTHON $VENV || { echo "Please ensure virtualenv is installed"; exit 2; }
     fi