diff --git a/core/modules/server/authenticators/header.js b/core/modules/server/authenticators/header.js
index 9d9990d31..cc1d6bdaf 100644
--- a/core/modules/server/authenticators/header.js
+++ b/core/modules/server/authenticators/header.js
@@ -37,7 +37,9 @@ HeaderAuthenticator.prototype.authenticateRequest = function(request,response,st
 		return false;
 	} else {
 		// authenticatedUsername will be undefined for anonymous users
-		state.authenticatedUsername = $tw.utils.decodeURIComponentSafe(username);
+		if(username) {
+			state.authenticatedUsername = $tw.utils.decodeURIComponentSafe(username);
+		}
 		return true;
 	}
 };