diff --git a/generate-firebase-json.js b/generate-firebase-json.js
index 02beaa7..33e57e5 100644
--- a/generate-firebase-json.js
+++ b/generate-firebase-json.js
@@ -42,19 +42,17 @@ const generateFirebaseJson = (
         .replace(/\.html/, '')
         .replace(/index/, '/')
         .replace(/404/, '**/*');
-    cspHeadersForSourceGlob = cspHeadersForSourceGlob.concat(
-        [
-            {
-                source: sourceGlob,
-                headers: [
-                    {
-                        key: 'Content-Security-Policy',
-                        value: builtPolicy,                    
-                    }  
-                ],
-            }
-        ]
-    );
+    cspHeadersForSourceGlob = [
+        {
+            source: sourceGlob,
+            headers: [
+                {
+                    key: 'Content-Security-Policy',
+                    value: builtPolicy,                    
+                }  
+            ],
+        }
+    ].concat(cspHeadersForSourceGlob);
 
     transformerFirebase(cspHeadersForSourceGlob);