diff --git a/src/backend/modern.lisp b/src/backend/modern.lisp
index 8766227..4362763 100644
--- a/src/backend/modern.lisp
+++ b/src/backend/modern.lisp
@@ -162,20 +162,20 @@ as a fallback when a keyword is not in *named-colors*.")
   (values))
 
 (defmethod backend-size ((b modern-backend))
-  (or ;; stty size with :input :interactive — opens /dev/tty for the
-      ;; child's stdin so stty can query the terminal via ioctl.
+  (or ;; ioctl on fd 0 (stdin) — the parent's own terminal, which IS
+      ;; the real controlling terminal when running from a shell.
       (multiple-value-bind (cols rows)
           (ignore-errors
-            (let* ((out (uiop:run-program '("stty" "size") :output :string
-                                          :input :interactive
-                                          :ignore-error-status t))
-                   (parts (and out (uiop:split-string
-                                     (string-trim '(#\newline #\space) out)))))
-              (when (and parts (= (length parts) 2))
-                (let ((r (parse-integer (first parts) :junk-allowed t))
-                      (c (parse-integer (second parts) :junk-allowed t)))
-                  (when (and r c (> r 0) (> c 0))
-                    (values c r))))))
+            (let ((winsize (sb-alien:make-alien sb-alien:unsigned-short 4)))
+              (unwind-protect
+                   (let ((ok (sb-unix:unix-ioctl 0 21523
+                                                 (sb-alien:alien-sap winsize))))
+                     (when ok
+                       (let ((c (sb-alien:deref winsize 1))
+                             (r (sb-alien:deref winsize 0)))
+                         (when (and c r (> c 0) (> r 0))
+                           (values c r)))))
+                (sb-alien:free-alien winsize))))
         (when (and cols rows (> cols 0) (> rows 0))
           (values cols rows)))
       ;; ioctl on stdout fd — fast, correct after SIGWINCH at runtime.
diff --git a/src/backend/simple.lisp b/src/backend/simple.lisp
index 33529a3..2fbfdb3 100644
--- a/src/backend/simple.lisp
+++ b/src/backend/simple.lisp
@@ -22,19 +22,19 @@
   (values))
 
 (defmethod backend-size ((b simple-backend))
-  (or ;; stty size with :input :interactive — opens /dev/tty.
+  (or ;; ioctl on fd 0 (stdin) — the parent's own terminal.
       (multiple-value-bind (cols rows)
           (ignore-errors
-            (let* ((out (uiop:run-program '("stty" "size") :output :string
-                                          :input :interactive
-                                          :ignore-error-status t))
-                   (parts (and out (uiop:split-string
-                                     (string-trim '(#\newline #\space) out)))))
-              (when (and parts (= (length parts) 2))
-                (let ((r (parse-integer (first parts) :junk-allowed t))
-                      (c (parse-integer (second parts) :junk-allowed t)))
-                  (when (and r c (> r 0) (> c 0))
-                    (values c r))))))
+            (let ((winsize (sb-alien:make-alien sb-alien:unsigned-short 4)))
+              (unwind-protect
+                   (let ((ok (sb-unix:unix-ioctl 0 21523
+                                                 (sb-alien:alien-sap winsize))))
+                     (when ok
+                       (let ((c (sb-alien:deref winsize 1))
+                             (r (sb-alien:deref winsize 0)))
+                         (when (and c r (> c 0) (> r 0))
+                           (values c r)))))
+                (sb-alien:free-alien winsize))))
         (when (and cols rows (> cols 0) (> rows 0))
           (values cols rows)))
       ;; ioctl on stdout fd — fast, correct after SIGWINCH at runtime.