diff --git a/src/backend/modern.lisp b/src/backend/modern.lisp
index d38e494..8766227 100644
--- a/src/backend/modern.lisp
+++ b/src/backend/modern.lisp
@@ -181,31 +181,29 @@ as a fallback when a keyword is not in *named-colors*.")
       ;; ioctl on stdout fd — fast, correct after SIGWINCH at runtime.
       (multiple-value-bind (cols rows)
           (ignore-errors
-            (let* ((+tiocgwinsz+ 21523)  ; 0x5413 on Linux
-                   (winsize (sb-alien:make-alien sb-alien:unsigned-short 4)))
+            (let* ((winsize (sb-alien:make-alien sb-alien:unsigned-short 4)))
               (unwind-protect
-                   (progn
-                     (sb-unix:unix-ioctl (sb-sys:fd-stream-fd (backend-output-stream b))
-                                         +tiocgwinsz+
-                                         (sb-alien:alien-sap winsize))
-                     (values (sb-alien:deref winsize 1)  ;; cols
-                             (sb-alien:deref winsize 0))) ;; rows
+                   (let ((ok (sb-unix:unix-ioctl
+                               (sb-sys:fd-stream-fd (backend-output-stream b))
+                               21523 (sb-alien:alien-sap winsize))))
+                     (when ok
+                       (values (sb-alien:deref winsize 1)  ;; cols
+                               (sb-alien:deref winsize 0)))) ;; rows
                 (sb-alien:free-alien winsize))))
         (when (and cols rows (> cols 0) (> rows 0))
           (values cols rows)))
-      ;; Direct ioctl on /dev/tty — opens the real controlling terminal.
+      ;; Direct ioctl on /dev/tty.
       (ignore-errors
-        (let ((tty-fd (sb-unix:unix-open "/dev/tty" 0 0)))  ; O_RDONLY
+        (let ((tty-fd (sb-unix:unix-open "/dev/tty" 0 0)))
           (when (and tty-fd (numberp tty-fd) (> tty-fd 0))
             (unwind-protect
                  (let* ((winsize (sb-alien:make-alien sb-alien:unsigned-short 4)))
-                   (sb-unix:unix-ioctl tty-fd 21523 (sb-alien:alien-sap winsize))
-                   (let ((cols (sb-alien:deref winsize 1))
-                         (rows (sb-alien:deref winsize 0)))
-                     (sb-alien:free-alien winsize)
-                     (when (and (integerp cols) (integerp rows)
-                                (> cols 0) (> rows 0))
-                       (values cols rows))))
+                   (let ((ok (sb-unix:unix-ioctl tty-fd 21523
+                                                 (sb-alien:alien-sap winsize))))
+                     (when ok
+                       (let ((cols (sb-alien:deref winsize 1))
+                             (rows (sb-alien:deref winsize 0)))
+                         (values cols rows)))))
               (sb-unix:unix-close tty-fd)))))
       (values 80 24)))
 
diff --git a/src/backend/simple.lisp b/src/backend/simple.lisp
index ecf9399..33529a3 100644
--- a/src/backend/simple.lisp
+++ b/src/backend/simple.lisp
@@ -40,31 +40,28 @@
       ;; ioctl on stdout fd — fast, correct after SIGWINCH at runtime.
       (multiple-value-bind (cols rows)
           (ignore-errors
-            (let* ((+tiocgwinsz+ 21523)
-                   (winsize (sb-alien:make-alien sb-alien:unsigned-short 4)))
+            (let* ((winsize (sb-alien:make-alien sb-alien:unsigned-short 4)))
               (unwind-protect
-                   (progn
-                     (sb-unix:unix-ioctl (sb-sys:fd-stream-fd
-                                          (backend-output-stream b))
-                                         +tiocgwinsz+
-                                         (sb-alien:alien-sap winsize))
-                     (values (sb-alien:deref winsize 1)
-                             (sb-alien:deref winsize 0)))
+                   (let ((ok (sb-unix:unix-ioctl
+                               (sb-sys:fd-stream-fd (backend-output-stream b))
+                               21523 (sb-alien:alien-sap winsize))))
+                     (when ok
+                       (values (sb-alien:deref winsize 1)
+                               (sb-alien:deref winsize 0))))
                 (sb-alien:free-alien winsize))))
         (when (and cols rows (> cols 0) (> rows 0))
           (values cols rows)))
       (ignore-errors
-        (let ((tty-fd (sb-unix:unix-open "/dev/tty" 0 0)))  ; O_RDONLY
+        (let ((tty-fd (sb-unix:unix-open "/dev/tty" 0 0)))
           (when (and tty-fd (numberp tty-fd) (> tty-fd 0))
             (unwind-protect
                  (let* ((winsize (sb-alien:make-alien sb-alien:unsigned-short 4)))
-                   (sb-unix:unix-ioctl tty-fd 21523 (sb-alien:alien-sap winsize))
-                   (let ((cols (sb-alien:deref winsize 1))
-                         (rows (sb-alien:deref winsize 0)))
-                     (sb-alien:free-alien winsize)
-                     (when (and (integerp cols) (integerp rows)
-                                (> cols 0) (> rows 0))
-                       (values cols rows))))
+                   (let ((ok (sb-unix:unix-ioctl tty-fd 21523
+                                                 (sb-alien:alien-sap winsize))))
+                     (when ok
+                       (values (sb-alien:deref winsize 1)
+                               (sb-alien:deref winsize 0))))
+                   (sb-alien:free-alien winsize))
               (sb-unix:unix-close tty-fd)))))
       (values 80 24)))