diff --git a/src/util/fs_helpers.cpp b/src/util/fs_helpers.cpp
index 42bdd8de30..33ab5b43ee 100644
--- a/src/util/fs_helpers.cpp
+++ b/src/util/fs_helpers.cpp
@@ -342,8 +342,7 @@ static std::optional<unsigned> StringToOctal(const std::string& str)
 
 static auto ConvertPermsToOctal(const std::string& str) noexcept -> std::optional<unsigned>
 {
-    // Don't permit setting special bits as they're not relevant to cookie files
-    if (str.length() == 3) return StringToOctal(str);
+    if ((str.length() == 3) || (str.length() == 4)) return StringToOctal(str);
     return std::nullopt;
 }
 
diff --git a/test/functional/rpc_users.py b/test/functional/rpc_users.py
index 5b721a77de..08584637ae 100755
--- a/test/functional/rpc_users.py
+++ b/test/functional/rpc_users.py
@@ -127,8 +127,9 @@ class HTTPBasicsTest(BitcoinTestFramework):
             "group": 0o640,
             "all": 0o644,
             "440": 0o440,
-            "640": 0o640,
+            "0640": 0o640,
             "444": 0o444,
+            "1660": 0o1660,
         }
 
         if os.name == 'nt':
@@ -137,7 +138,7 @@ class HTTPBasicsTest(BitcoinTestFramework):
         self.log.info('Check cookie file permissions can be set using -rpccookieperms')
 
         cookie_file_path = self.nodes[1].chain_path / '.cookie'
-        PERM_BITS_UMASK = 0o777
+        PERM_BITS_UMASK = 0o7777
 
         def test_perm(perm: Optional[str]):
             if not perm: