diff --git a/NEWS b/NEWS
index 6b36ece15..0ec26e39f 100644
--- a/NEWS
+++ b/NEWS
@@ -1,6 +1,7 @@
 ver 0.23.2 (not yet released)
 * neighbor
   - mention failed plugin name in error message
+* fix crash with libfmt versions older than 7
 
 ver 0.23.1 (2021/10/19)
 * protocol
diff --git a/src/client/Response.cxx b/src/client/Response.cxx
index cda9e4969..4bfe10069 100644
--- a/src/client/Response.cxx
+++ b/src/client/Response.cxx
@@ -66,7 +66,11 @@ Response::WriteBinary(ConstBuffer<void> payload) noexcept
 void
 Response::Error(enum ack code, const char *msg) noexcept
 {
-	FmtError(code, FMT_STRING("{}"), msg);
+	Fmt(FMT_STRING("ACK [{}@{}] {{{}}} "),
+	    (int)code, list_index, command);
+
+	Write(msg);
+	Write("\n");
 }
 
 void