diff --git a/man2/gettid.2 b/man2/gettid.2
index ccf9ec1a2..daed62cc7 100644
--- a/man2/gettid.2
+++ b/man2/gettid.2
@@ -68,6 +68,18 @@ Glibc does not provide a wrapper for this system call; call it using
 The thread ID returned by this call is not the same thing as a
 POSIX thread ID (i.e., the opaque value returned by
 .BR pthread_self (3)).
+
+In a new thread group created by a
+.BR clone (2)
+call that does not specify the
+.BR CLONE_THREAD
+flag (or, equivalently, a new process created by
+.BR fork (2)),
+the new process is a thread group leader,
+and its thread group ID (the value returned by
+.BR getpid (2))
+is the same as its thread ID (the value returned by
+.BR gettid ()).
 .SH SEE ALSO
 .BR capget (2),
 .BR clone (2),