diff --git a/drain/drain.py b/drain/drain.py
index d650a0d..330be6a 100755
--- a/drain/drain.py
+++ b/drain/drain.py
@@ -292,8 +292,8 @@ def try_for_htlc_fee(plugin, payload, peer_id, amount, chunk, spendable_before):
             if not result.get('status') == 'complete':
                 return False  # should not happen, but maybe API changes
             payload['success_msg'].append(f"{amount + fees}msat sent over {len(route)} "
-                                          "hops to {payload['command']} {amount}msat "
-                                          "[{chunk + 1}/{payload['chunks']}")
+                                          f"hops to {payload['command']} {amount}msat "
+                                          f"[{chunk + 1}/{payload['chunks']}")
             # we need to wait for HTLC to resolve, so remaining amounts
             # can be calculated correctly for the next chunk
             wait_ours(plugin, payload['scid'], ours)