diff --git a/types/src/lib.rs b/types/src/lib.rs
index b8b6bc0b..5506979d 100644
--- a/types/src/lib.rs
+++ b/types/src/lib.rs
@@ -3724,11 +3724,7 @@ impl TypeRef {
 
     pub fn as_mut(self, db: &Database) -> Self {
         match self {
-            TypeRef::Owned(
-                id @ TypeId::RigidTypeParameter(pid)
-                | id @ TypeId::TypeParameter(pid),
-            )
-            | TypeRef::Any(
+            TypeRef::Any(
                 id @ TypeId::RigidTypeParameter(pid)
                 | id @ TypeId::TypeParameter(pid),
             ) => {
@@ -5258,7 +5254,14 @@ mod tests {
             uni(instance(int)).as_mut(&db),
             TypeRef::UniMut(instance(int))
         );
-        assert_eq!(owned(rigid(param1)).as_mut(&db), immutable(rigid(param1)));
+
+        assert_eq!(any(rigid(param1)).as_mut(&db), immutable(rigid(param1)));
+        assert_eq!(
+            owned(parameter(param1)).as_mut(&db),
+            mutable(parameter(param1))
+        );
+
+        assert_eq!(owned(rigid(param1)).as_mut(&db), mutable(rigid(param1)));
         assert_eq!(owned(rigid(param2)).as_mut(&db), mutable(rigid(param2)));
         assert_eq!(
             owned(parameter(param2)).as_mut(&db),