diff --git a/NEWS b/NEWS
index bde051dee660..d72267e9cc1c 100644
--- a/NEWS
+++ b/NEWS
@@ -40,6 +40,10 @@ PHP                                                                        NEWS
   . Fixed bug GH-23619 (cryptic error on servers that don't support TLS
     session resumption on data connection). (ndossche)
 
+- Hash:
+  . Fixed mhash_keygen_s2k() truncating a $length above INT_MAX instead of
+    throwing a ValueError. (Marc Bennewitz)
+
 - Intl:
   . Fixed cloning IntlDateFormatter and MessageFormatter losing PHP-side state
     such as dateType, timeType, calendar and the message pattern.
diff --git a/ext/hash/hash.c b/ext/hash/hash.c
index 93401852ad3d..615a8325fc5f 100644
--- a/ext/hash/hash.c
+++ b/ext/hash/hash.c
@@ -1294,12 +1294,18 @@ PHP_FUNCTION(mhash_keygen_s2k)
 		RETURN_THROWS();
 	}
 
-	bytes = (int)l_bytes;
-	if (bytes <= 0){
+	if (l_bytes <= 0) {
 		zend_argument_value_error(4, "must be a greater than 0");
 		RETURN_THROWS();
 	}
 
+	if (ZEND_LONG_INT_OVFL(l_bytes)) {
+		zend_argument_value_error(4, "must be less than or equal to %d", INT_MAX);
+		RETURN_THROWS();
+	}
+
+	bytes = (int)l_bytes;
+
 	salt_len = MIN(salt_len, SALT_SIZE);
 
 	memcpy(padded_salt, salt, salt_len);
diff --git a/ext/hash/tests/gh23950.phpt b/ext/hash/tests/gh23950.phpt
new file mode 100644
index 000000000000..d9aa7dea4081
--- /dev/null
+++ b/ext/hash/tests/gh23950.phpt
@@ -0,0 +1,29 @@
+--TEST--
+MHash: GH-23950 (mhash_keygen_s2k() $length must not be truncated to int)
+--SKIPIF--
+<?php
+if (!function_exists('mhash')) die('skip mhash compatibility layer not available');
+if (PHP_INT_SIZE == 4) die('skip only where a PHP integer is wider than an int');
+?>
+--FILE--
+<?php
+foreach ([2**31, 2**32, 2**32 + 16, PHP_INT_MAX] as $length) {
+    try {
+        var_dump(strlen(mhash_keygen_s2k(1, 'password', 'salt', $length)));
+    } catch (Throwable $e) {
+        echo $e::class, ': ', $e->getMessage(), "\n";
+    }
+}
+?>
+--EXPECTF--
+Deprecated: Function mhash_keygen_s2k() is deprecated since 8.1 in %s on line %d
+ValueError: mhash_keygen_s2k(): Argument #4 ($length) must be less than or equal to 2147483647
+
+Deprecated: Function mhash_keygen_s2k() is deprecated since 8.1 in %s on line %d
+ValueError: mhash_keygen_s2k(): Argument #4 ($length) must be less than or equal to 2147483647
+
+Deprecated: Function mhash_keygen_s2k() is deprecated since 8.1 in %s on line %d
+ValueError: mhash_keygen_s2k(): Argument #4 ($length) must be less than or equal to 2147483647
+
+Deprecated: Function mhash_keygen_s2k() is deprecated since 8.1 in %s on line %d
+ValueError: mhash_keygen_s2k(): Argument #4 ($length) must be less than or equal to 2147483647