diff --git a/src/generate.rs b/src/generate.rs
index cd754d6..472382d 100644
--- a/src/generate.rs
+++ b/src/generate.rs
@@ -741,6 +741,9 @@ impl<'a> RouteSink<'a> {
         nsid: &str,
         limit_override: Option<&str>,
     ) -> bool {
+        if key.mutability() != Mutability::Immutable {
+            return false;
+        }
         let Some(response) = self.reuse_prior(repo_prior, key, nsid, limit_override) else {
             return false;
         };