diff --git a/Documentation/technical/api-error-handling.txt b/Documentation/technical/api-error-handling.txt
index ceeedd485c..8be4f4d0d6 100644
--- a/Documentation/technical/api-error-handling.txt
+++ b/Documentation/technical/api-error-handling.txt
@@ -1,8 +1,11 @@
 Error reporting in git
 ======================
 
-`die`, `usage`, `error`, and `warning` report errors of various
-kinds.
+`BUG`, `die`, `usage`, `error`, and `warning` report errors of
+various kinds.
+
+- `BUG` is for failed internal assertions that should never happen,
+  i.e. a bug in git itself.
 
 - `die` is for fatal application errors.  It prints a message to
   the user and exits with status 128.
@@ -20,6 +23,9 @@ kinds.
   without running into too many problems.  Like `error`, it
   returns -1 after reporting the situation to the caller.
 
+These reports will be logged via the trace2 facility. See the "error"
+event in link:api-trace2.txt[trace2 API].
+
 Customizable error handlers
 ---------------------------
 
diff --git a/Documentation/technical/api-trace2.txt b/Documentation/technical/api-trace2.txt
index c65ffafc48..3f52f981a2 100644
--- a/Documentation/technical/api-trace2.txt
+++ b/Documentation/technical/api-trace2.txt
@@ -465,7 +465,7 @@ completed.)
 ------------
 
 `"error"`::
-	This event is emitted when one of the `error()`, `die()`,
+	This event is emitted when one of the `BUG()`, `error()`, `die()`,
 	`warning()`, or `usage()` functions are called.
 +
 ------------
diff --git a/usage.c b/usage.c
index 1b206de36d..c7d233b0de 100644
--- a/usage.c
+++ b/usage.c
@@ -55,12 +55,13 @@ static NORETURN void usage_builtin(const char *err, va_list params)
 	exit(129);
 }
 
+/*
+ * We call trace2_cmd_error_va() in the below functions first and
+ * expect it to va_copy 'params' before using it (because an 'ap' can
+ * only be walked once).
+ */
 static NORETURN void die_builtin(const char *err, 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(err, params);
 
 	vreportf("fatal: ", err, params);
@@ -70,10 +71,6 @@ static NORETURN void die_builtin(const char *err, va_list params)
 
 static void error_builtin(const char *err, 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(err, params);
 
 	vreportf("error: ", err, params);
@@ -81,10 +78,6 @@ 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);