diff --git a/ext/standard/file.c b/ext/standard/file.c
index a7b73f1fe56eb..ca24b34eb8c4f 100644
--- a/ext/standard/file.c
+++ b/ext/standard/file.c
@@ -1087,6 +1087,11 @@ PHP_FUNCTION(mkdir)
 		Z_PARAM_RESOURCE_OR_NULL(zcontext)
 	ZEND_PARSE_PARAMETERS_END();
 
+	if (mode < 0 || (mode & ~07777)) {
+		zend_argument_value_error(2, "must be between 0 and 0o7777");
+		RETURN_THROWS();
+	}
+
 	context = php_stream_context_from_zval(zcontext, 0);
 
 	RETURN_BOOL(php_stream_mkdir(dir, (int)mode, (recursive ? PHP_STREAM_MKDIR_RECURSIVE : 0) | REPORT_ERRORS, context));
diff --git a/ext/standard/tests/file/mkdir_invalid_mode.phpt b/ext/standard/tests/file/mkdir_invalid_mode.phpt
new file mode 100644
index 0000000000000..c36a8f6c4b846
--- /dev/null
+++ b/ext/standard/tests/file/mkdir_invalid_mode.phpt
@@ -0,0 +1,34 @@
+--TEST--
+mkdir(): invalid mode
+--FILE--
+<?php
+$testCases = [
+    1000000,    // way too large
+    -1,         // negative
+    0o10000,    // above 0o7777
+    0x1FFFF,    // hex, still too large
+    12345,      // arbitrary invalid
+];
+
+foreach ($testCases as $mode) {
+    try {
+        echo "Testing mode: $mode\n";
+        mkdir(__DIR__ . "/testdir_$mode", $mode);
+    } catch (ValueError $e) {
+        echo $e->getMessage(), PHP_EOL;
+    } catch (Exception $e) {
+        echo "Other exception: ", $e->getMessage(), PHP_EOL;
+    }
+}
+?>
+--EXPECT--
+Testing mode: 1000000
+mkdir(): Argument #2 ($permissions) must be between 0 and 0o7777
+Testing mode: -1
+mkdir(): Argument #2 ($permissions) must be between 0 and 0o7777
+Testing mode: 4096
+mkdir(): Argument #2 ($permissions) must be between 0 and 0o7777
+Testing mode: 131071
+mkdir(): Argument #2 ($permissions) must be between 0 and 0o7777
+Testing mode: 12345
+mkdir(): Argument #2 ($permissions) must be between 0 and 0o7777