diff --git a/Documentation/technical/api-trace2.txt b/Documentation/technical/api-trace2.txt
index 6b6085585d..c65ffafc48 100644
--- a/Documentation/technical/api-trace2.txt
+++ b/Documentation/technical/api-trace2.txt
@@ -466,7 +466,7 @@ completed.)
 
 `"error"`::
 	This event is emitted when one of the `error()`, `die()`,
-	or `usage()` functions are called.
+	`warning()`, or `usage()` functions are called.
 +
 ------------
 {
diff --git a/usage.c b/usage.c
index 58fb5fff5f..7c58b2688c 100644
--- a/usage.c
+++ b/usage.c
@@ -81,6 +81,12 @@ static void error_builtin(const char *err, va_list params)
 
 static void warn_builtin(const char *warn, va_list params)
 {
+	/*
+	 * We call this trace2 function first and expect it to va_copy 'params'
+	 * before using it (because an 'ap' can only be walked once).
+	 */
+	trace2_cmd_error_va(warn, params);
+
 	vreportf("warning: ", warn, params);
 }