diff --git a/src/headers.js b/src/headers.js
index 9355f0d..d616a41 100644
--- a/src/headers.js
+++ b/src/headers.js
@@ -17,9 +17,10 @@ function getLDHeaders(platform, options) {
   if (tagKeys.length) {
     h['x-launchdarkly-tags'] = tagKeys
       .sort()
-      .flatMap(
+      .map(
         key => (Array.isArray(tags[key]) ? tags[key].sort().map(value => `${key}/${value}`) : [`${key}/${tags[key]}`])
       )
+      .reduce((flattened, item) => flattened.concat(item), [])
       .join(' ');
   }
   return h;