diff --git a/tools/fork/name-allowlist.txt b/tools/fork/name-allowlist.txt
index 6f108a43..ccabf55f 100644
--- a/tools/fork/name-allowlist.txt
+++ b/tools/fork/name-allowlist.txt
@@ -23,6 +23,12 @@ crates/migration/src/lib.rs	"STALWART_SPAM_CLASSIFIER_MODEL.lz4"
 crates/migration/src/lib.rs	"STALWART_SPAM_TRAIN_DATA.lz4"
 crates/types/src/branding.rs	"STALWART"
 
+# Pre-rename Sieve extension names, accepted as aliases so scripts written
+# for upstream still compile when edited. Never advertised; the test proves it.
+vendor/sieve-rs/src/compiler/grammar/mod.rs	"vnd.stalwart.while"
+vendor/sieve-rs/src/compiler/grammar/mod.rs	"vnd.stalwart.expressions"
+vendor/sieve-rs/src/compiler/grammar/mod.rs	"require [\\\"vnd.stalwart.expressions\\\", \\\"variables\\\"];\\nlet \\\"n\\\" \\\"1 + 2\\\";\\n"
+
 # Upstream's old default rules source, read only to treat it as unset: the
 # server uses the rules bundled with it (resources/spam-filter/).
 crates/common/src/manager/spam_rules.rs	"https://github.com/stalwartlabs/spam-filter/releases/latest/download/spam-filter-rules.json.gz"
diff --git a/vendor/sieve-rs/VENDORED.md b/vendor/sieve-rs/VENDORED.md
index 2cdf7a6d..d5e40258 100644
--- a/vendor/sieve-rs/VENDORED.md
+++ b/vendor/sieve-rs/VENDORED.md
@@ -11,7 +11,11 @@ Every changed file carries the AGPL 5(a) notice in its header.
 
 - `src/compiler/grammar/mod.rs`: the extensions scripts `require` and
   ManageSieve advertises are `vnd.inbuxa.while` and
-  `vnd.inbuxa.expressions`.
+  `vnd.inbuxa.expressions`. The pre-rename `vnd.stalwart.*` spellings are
+  still accepted, never advertised, so a script written for upstream compiles
+  when it's edited. Without them, the name is treated as an unknown extension
+  and `let` or `eval` fails with "Undeclared capability". The
+  `legacy_extension_names` tests cover both.
 - `src/runtime/mod.rs`: the default `environment "name"` is `inbuxa Sieve`
   (the server sets its own name on both of its runtimes anyway), and the
   test-only capability is `vnd.inbuxa.testsuite`.
diff --git a/vendor/sieve-rs/src/compiler/grammar/mod.rs b/vendor/sieve-rs/src/compiler/grammar/mod.rs
index 59a9f90b..f9f4c187 100644
--- a/vendor/sieve-rs/src/compiler/grammar/mod.rs
+++ b/vendor/sieve-rs/src/compiler/grammar/mod.rs
@@ -732,5 +732,35 @@ fn lookup_capabilities(input: &str) -> Option<Capability> {
         // Extensions
         "vnd.inbuxa.while" => Capability::While,
         "vnd.inbuxa.expressions" => Capability::Expressions,
+        // The pre-rename spellings, so scripts written for upstream still
+        // compile when they're edited. They're never advertised.
+        "vnd.stalwart.while" => Capability::While,
+        "vnd.stalwart.expressions" => Capability::Expressions,
     )
 }
+
+#[cfg(test)]
+mod legacy_extension_names {
+    use super::Capability;
+    use crate::Compiler;
+
+    #[test]
+    fn old_spelling_parses_new_spelling_is_shown() {
+        for (old, new) in [
+            ("vnd.stalwart.while", "vnd.inbuxa.while"),
+            ("vnd.stalwart.expressions", "vnd.inbuxa.expressions"),
+        ] {
+            let parsed = Capability::parse(old);
+            assert_eq!(parsed.to_string(), new);
+            assert_eq!(parsed, Capability::parse(new));
+        }
+    }
+
+    #[test]
+    fn script_using_old_spelling_compiles() {
+        let script = b"require [\"vnd.stalwart.expressions\", \"variables\"];\nlet \"n\" \"1 + 2\";\n";
+        Compiler::new()
+            .compile(script)
+            .expect("a script requiring the pre-rename name compiles");
+    }
+}