diff --git a/librb/rbRadios.py b/librb/rbRadios.py
index a018215..25af8d5 100644
--- a/librb/rbRadios.py
+++ b/librb/rbRadios.py
@@ -11,9 +11,9 @@ def request(endpoint, **kwargs):
     fmt = kwargs.get("format", "json")
 
     if fmt == "xml":
-        content_type = f"application/{fmt}"
+        content_type = "application/%s" % fmt
     else:
-        content_type = f"application/{fmt}"
+        content_type = "application/%s" % fmt
 
     headers = {"content-type": content_type, "User-Agent": "pyradios/dev"}