diff --git a/include/stdlib.h b/include/stdlib.h
--- a/include/stdlib.h
+++ b/include/stdlib.h
@@ -242,8 +242,18 @@
 char	*ptsname(int);
 int	 unlockpt(int);
 #endif /* __XSI_VISIBLE */
-#if __BSD_VISIBLE
-/* ptsname_r will be included in POSIX issue 8 */
+/*
+ * ptsname_r is included in POSIX issue 8 (IEEE Std 1003.1-2024).
+ * posix_ptsname_r() is the POSIX-compliant interface (returns error number).
+ * ptsname_r() is the traditional FreeBSD interface (returns -1 and sets errno).
+ * When _POSIX_C_SOURCE >= 202405, ptsname_r is aliased to posix_ptsname_r.
+ */
+#if (defined(_POSIX_C_SOURCE) && _POSIX_C_SOURCE >= 202405) || __BSD_VISIBLE
+int	 posix_ptsname_r(int, char *, size_t);
+#endif
+#if defined(_POSIX_C_SOURCE) && _POSIX_C_SOURCE >= 202405
+#define	ptsname_r	posix_ptsname_r
+#elif __BSD_VISIBLE
 int	 ptsname_r(int, char *, size_t);
 #endif
 
diff --git a/lib/libc/stdlib/Symbol.map b/lib/libc/stdlib/Symbol.map
--- a/lib/libc/stdlib/Symbol.map
+++ b/lib/libc/stdlib/Symbol.map
@@ -133,6 +133,7 @@
 
 FBSD_1.9 {
 	memalignment;
+	posix_ptsname_r;
 	recallocarray;
 	strtonumx;
 	tdestroy;
diff --git a/lib/libc/stdlib/ptsname.3 b/lib/libc/stdlib/ptsname.3
--- a/lib/libc/stdlib/ptsname.3
+++ b/lib/libc/stdlib/ptsname.3
@@ -29,7 +29,7 @@
 .\" NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
 .\" SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 .\"
-.Dd October 14, 2023
+.Dd February 15, 2026
 .Dt PTSNAME 3
 .Os
 .Sh NAME
@@ -116,15 +116,21 @@
 The
 .Fn ptsname_r
 function returns the value 0 if successful;
-otherwise a nonzero value is returned and the global variable
+otherwise an error number is returned to indicate the error.
+.Pp
+As a
+.Fx
+extension, the global variable
 .Va errno
-is set to indicate the error.
-Note:
+is also set to indicate the error for convenience,
+even though
+.St -p1003.1-2024
+only requires the error number to be returned.
+.Pp
+When compiled without POSIX.1-2024 visibility,
 .Fn ptsname_r
-was previously documented as returning -1 on error.
-In the future it will be changed to return an error number, for POSIX
-compatibility.
-Therefore, callers should not check for -1.
+uses the legacy FreeBSD ABI and returns -1 on error while setting
+.Va errno .
 .Sh ERRORS
 The
 .Fn grantpt ,
@@ -141,7 +147,14 @@
 is not a valid open file descriptor.
 .It Bq Er EINVAL
 .Fa fildes
-is not a master pseudo-terminal device.
+is not a master pseudo-terminal device,
+or
+.Po
+for
+.Fn ptsname_r
+.Pc
+.Fa buffer
+is a null pointer.
 .El
 .Pp
 In addition, the
@@ -173,6 +186,16 @@
 function conforms to
 .St -p1003.1-2008 .
 .Pp
+The
+.Fn ptsname_r
+function conforms to
+.St -p1003.1-2024 ,
+except that
+.Fx
+also sets
+.Va errno
+as an extension.
+.Pp
 This implementation of
 .Fn grantpt
 and
@@ -195,3 +218,14 @@
 .Fn unlockpt
 functions appeared in
 .Fx 5.0 .
+.Pp
+The
+.Fn ptsname_r
+function appeared in
+.Fx 13.0 .
+In
+.Fx 16.0 ,
+the function was changed to return the error number directly
+to conform with
+.St -p1003.1-2024 ,
+while maintaining binary compatibility with earlier versions.
diff --git a/lib/libc/stdlib/ptsname.c b/lib/libc/stdlib/ptsname.c
--- a/lib/libc/stdlib/ptsname.c
+++ b/lib/libc/stdlib/ptsname.c
@@ -67,21 +67,27 @@
 __strong_reference(__isptmaster, unlockpt);
 
 /*
- * ptsname_r(): return the pathname of the slave pseudo-terminal device
- *              associated with the specified master.
+ * posix_ptsname_r(): return the pathname of the slave pseudo-terminal device
+ *                    associated with the specified master.
+ *                    POSIX-compliant: returns 0 on success, error number on failure.
  */
 int
-__ptsname_r(int fildes, char *buffer, size_t buflen)
+posix_ptsname_r(int fildes, char *buffer, size_t buflen)
 {
 
+	if (buffer == NULL) {
+		errno = EINVAL;
+		return (errno);
+	}
+
 	if (buflen <= sizeof(_PATH_DEV)) {
 		errno = ERANGE;
-		return (-1);
+		return (errno);
 	}
 
 	/* Make sure fildes points to a master device. */
 	if (__isptmaster(fildes) != 0)
-		return (-1);
+		return (errno);
 
 	memcpy(buffer, _PATH_DEV, sizeof(_PATH_DEV));
 	buffer += sizeof(_PATH_DEV) - 1;
@@ -90,13 +96,23 @@
 	if (fdevname_r(fildes, buffer, buflen) == NULL) {
 		if (errno == EINVAL)
 			errno = ERANGE;
-		return (-1);
+		return (errno);
 	}
 
 	return (0);
 }
 
-__strong_reference(__ptsname_r, ptsname_r);
+/*
+ * Prior to FreeBSD 16 we returned -1 on error, not an error number as is now
+ * specified by POSIX.
+ */
+int
+ptsname_r(int fildes, char *buffer, size_t buflen)
+{
+	if (posix_ptsname_r(fildes, buffer, buflen) != 0)
+		return (-1);
+	return (0);
+}
 
 /*
  * ptsname():  return the pathname of the slave pseudo-terminal device
@@ -107,7 +123,7 @@
 {
 	static char pt_slave[sizeof(_PATH_DEV) + SPECNAMELEN];
 
-	if (__ptsname_r(fildes, pt_slave, sizeof(pt_slave)) == 0)
+	if (posix_ptsname_r(fildes, pt_slave, sizeof(pt_slave)) == 0)
 		return (pt_slave);
 
 	return (NULL);