diff --git a/attach.c b/attach.c
index 5e8453e..c2986a8 100644
--- a/attach.c
+++ b/attach.c
@@ -256,6 +256,34 @@ int replay_session_log(int saved_errno)
 	return 1;
 }
 
+/* Returns 1 if sockname appears in the current process's atch session
+** ancestry chain (SESSION_ENVVAR, colon-separated, outermost first).
+** Shared by attach_main and kill_main to refuse both direct self-
+** attach/self-kill and indirect loops like A -> B -> A. */
+static int session_in_ancestry(const char *sockname)
+{
+	const char *chain = getenv(SESSION_ENVVAR);
+	size_t slen;
+	const char *p;
+
+	if (!chain || !*chain)
+		return 0;
+
+	slen = strlen(sockname);
+	p = chain;
+	while (*p) {
+		const char *colon = strchr(p, ':');
+		size_t tlen = colon ? (size_t)(colon - p) : strlen(p);
+
+		if (tlen == slen && strncmp(p, sockname, tlen) == 0)
+			return 1;
+		if (!colon)
+			break;
+		p = colon + 1;
+	}
+	return 0;
+}
+
 int attach_main(int noerror)
 {
 	struct packet pkt;
@@ -264,35 +292,13 @@ int attach_main(int noerror)
 	int s;
 
 	/* Refuse to attach to any session in our ancestry chain (catches both
-	 * direct self-attach and indirect loops like A -> B -> A).
-	 * SESSION_ENVVAR is the colon-separated chain, so scanning it covers
-	 * all ancestors. */
-	{
-		const char *tosearch = getenv(SESSION_ENVVAR);
-
-		if (tosearch && *tosearch) {
-			size_t slen = strlen(sockname);
-			const char *p = tosearch;
-
-			while (*p) {
-				const char *colon = strchr(p, ':');
-				size_t tlen =
-				    colon ? (size_t)(colon - p) : strlen(p);
-
-				if (tlen == slen
-				    && strncmp(p, sockname, tlen) == 0) {
-					if (!noerror)
-						printf
-						    ("%s: cannot attach to session '%s' from within itself\n",
-						     progname,
-						     session_shortname());
-					return 1;
-				}
-				if (!colon)
-					break;
-				p = colon + 1;
-			}
-		}
+	 * direct self-attach and indirect loops like A -> B -> A). */
+	if (session_in_ancestry(sockname)) {
+		if (!noerror)
+			printf
+			    ("%s: cannot attach to session '%s' from within itself\n",
+			     progname, session_shortname());
+		return 1;
 	}
 
 	/* Attempt to open the socket. Don't display an error if noerror is
@@ -537,6 +543,17 @@ int kill_main(int force)
 	const char *name = session_shortname();
 	int i;
 
+	/* Refuse to kill/stop any session in our ancestry chain — same check
+	 * as attach_main, see session_in_ancestry(). Previously unchecked:
+	 * killing your own controlling session from within it just made the
+	 * signal race the caller's own exit, with no explanatory message. */
+	if (session_in_ancestry(sockname)) {
+		printf
+		    ("%s: cannot kill/stop session '%s' from within itself — run this from another session or terminal instead\n",
+		     progname, name);
+		return 1;
+	}
+
 	signal(SIGPIPE, SIG_IGN);
 
 	if (force) {
diff --git a/tests/test.sh b/tests/test.sh
index 5848d71..7e274da 100644
--- a/tests/test.sh
+++ b/tests/test.sh
@@ -276,6 +276,37 @@ run "$ATCH" kill -f s-noexist-force
 assert_exit     "kill -f: nonexistent → exit 1"      1 "$rc"
 assert_contains "kill -f: nonexistent → message"     "does not exist" "$out"
 
+# kill/stop refuses to target the session in the caller's own ancestry chain
+# (ATCH_SESSION), same guard as attach's self-attach check.
+# NOTE: `VAR=val run ...` would leak VAR into the rest of this script, since
+# `run` is a shell function -- a temporary assignment before a function call
+# persists after it returns (POSIX behavior, unlike prefixing an external
+# command). Export/unset explicitly instead.
+"$ATCH" start s-selfkill sleep 999
+export ATCH_SESSION="$HOME/.cache/atch/s-selfkill"
+run "$ATCH" kill s-selfkill
+unset ATCH_SESSION
+assert_exit     "kill: self → exit 1"                1 "$rc"
+assert_contains "kill: self → message"               "from within itself" "$out"
+tidy s-selfkill
+
+"$ATCH" start s-selfkillf sleep 999
+export ATCH_SESSION="$HOME/.cache/atch/s-selfkillf"
+run "$ATCH" kill -f s-selfkillf
+unset ATCH_SESSION
+assert_exit     "kill -f: self → exit 1"             1 "$rc"
+assert_contains "kill -f: self → message"            "from within itself" "$out"
+tidy s-selfkillf
+
+# a mismatched ATCH_SESSION (different session, not an ancestor) must not
+# trip the guard -- only an exact ancestry-chain match refuses the kill
+"$ATCH" start s-notself sleep 999
+export ATCH_SESSION="$HOME/.cache/atch/some-other-session"
+run "$ATCH" kill s-notself
+unset ATCH_SESSION
+assert_exit     "kill: non-ancestor session unaffected → exit 0" 0 "$rc"
+assert_contains "kill: non-ancestor session unaffected → stopped" "stopped" "$out"
+
 # ── 6. clear command ─────────────────────────────────────────────────────────
 
 run "$ATCH" clear