diff --git a/crates/engine/src/plugins.rs b/crates/engine/src/plugins.rs
index 0159a924..18fd64ef 100644
--- a/crates/engine/src/plugins.rs
+++ b/crates/engine/src/plugins.rs
@@ -393,6 +393,7 @@ pub(crate) fn register(s: &mut Session, entry: InstalledPlugin, wasm: Vec<u8>) -
     match list.iter_mut().find(|x| x.manifest.id == id) {
         Some(slot) => {
             *slot = entry;
+            s.prefs.plugin_settings.remove(&id);
             true
         }
         None => {
diff --git a/crates/engine/src/plugins_tests.rs b/crates/engine/src/plugins_tests.rs
index 51c997a5..172fd477 100644
--- a/crates/engine/src/plugins_tests.rs
+++ b/crates/engine/src/plugins_tests.rs
@@ -406,3 +406,13 @@ fn a_full_undo_history_keeps_its_steps_and_tampered_manifests_are_refused() {
     s.prefs.plugins[0].manifest.main = "../../elsewhere.wasm".into();
     assert!(matches!(s.execute("plugin.run", &json!({"id": "org.test.many"})), Err(EngineError::BadParams { .. })));
 }
+
+#[test]
+fn reinstalling_under_an_existing_id_drops_the_old_settings() {
+    let mut s = Session::new();
+    let m = manifest("org.test.reuse", "read", &[]);
+    install(&mut s, m.clone(), &script(&[], OnRefusal::Fail, ""));
+    s.prefs.plugin_settings.entry("org.test.reuse".into()).or_default().insert("key".into(), json!("v"));
+    install(&mut s, m, &script(&[], OnRefusal::Fail, ""));
+    assert!(!s.prefs.plugin_settings.contains_key("org.test.reuse"), "{:?}", s.prefs.plugin_settings);
+}