diff --git a/core/Dockerfile b/core/Dockerfile
index a956f9c8..61659799 100644
--- a/core/Dockerfile
+++ b/core/Dockerfile
@@ -17,7 +17,7 @@ RUN apk update \
                    mailman==3.3.1 \
                    mailman-hyperkitty==1.1.0 \
                    pymysql \
-		   dnspython<2.0 \
+		   'dnspython<2.0' \
     && apk del build-deps \
     && adduser -S mailman