diff --git a/fs/exec.c b/fs/exec.c
index 4d38ad0..3234a0c 100644
--- a/fs/exec.c
+++ b/fs/exec.c
@@ -678,6 +678,18 @@
 		while (leader->exit_state != EXIT_ZOMBIE)
 			yield();
 
+		/*
+		 * The only record we have of the real-time age of a
+		 * process, regardless of execs it's done, is start_time.
+		 * All the past CPU time is accumulated in signal_struct
+		 * from sister threads now dead.  But in this non-leader
+		 * exec, nothing survives from the original leader thread,
+		 * whose birth marks the true age of this process now.
+		 * When we take on its identity by switching to its PID, we
+		 * also take its birthdate (always earlier than our own).
+		 */
+		current->start_time = leader->start_time;
+
 		spin_lock(&leader->proc_lock);
 		spin_lock(&current->proc_lock);
 		proc_dentry1 = proc_pid_unhash(current);