diff --git a/src/comp/middle/trans.rs b/src/comp/middle/trans.rs
index e4a35a8d6b6..bae944659d9 100644
--- a/src/comp/middle/trans.rs
+++ b/src/comp/middle/trans.rs
@@ -958,10 +958,13 @@ fn get_derived_tydesc(cx: &@block_ctxt, t: ty::t, escapes: bool,
 
         // If the tydesc escapes in this context, the cached derived
         // tydesc also has to be one that was marked as escaping.
-        if !(escapes && !info.escapes) { ret rslt(cx, info.lltydesc); }
+        if !(escapes && !info.escapes) && storage == tps_normal {
+            ret rslt(cx, info.lltydesc);
+        }
       }
       none. {/* fall through */ }
     }
+
     bcx_ccx(cx).stats.n_derived_tydescs += 1u;
     let bcx = new_raw_block_ctxt(cx.fcx, cx.fcx.llderivedtydescs);
     let tys = linearize_ty_params(bcx, t);
diff --git a/src/rt/rust_crate_cache.cpp b/src/rt/rust_crate_cache.cpp
index ba5a104b024..035715d219f 100644
--- a/src/rt/rust_crate_cache.cpp
+++ b/src/rt/rust_crate_cache.cpp
@@ -1,5 +1,6 @@
 
 #include "rust_internal.h"
+#include <algorithm>
 
 type_desc *
 rust_crate_cache::get_type_desc(size_t size,
@@ -14,6 +15,10 @@ rust_crate_cache::get_type_desc(size_t size,
     HASH_FIND(hh, this->type_descs, descs, keysz, td);
     if (td) {
         DLOG(sched, cache, "rust_crate_cache::get_type_desc hit");
+
+        // FIXME: This is a gross hack.
+        td->n_obj_params = std::max(td->n_obj_params, n_obj_params);
+
         return td;
     }
     DLOG(sched, cache, "rust_crate_cache::get_type_desc miss");
diff --git a/src/rt/rust_shape.h b/src/rt/rust_shape.h
index 0302338e26d..e8a30d5874a 100644
--- a/src/rt/rust_shape.h
+++ b/src/rt/rust_shape.h
@@ -259,6 +259,9 @@ public:
     // Creates type parameters from a type descriptor.
     static inline type_param *from_tydesc(const type_desc *tydesc,
                                           arena &arena) {
+        if (tydesc->n_obj_params) {
+            // TODO
+        }
         return make(tydesc->first_param, tydesc->n_params, arena);
     }
 };