diff --git a/src/rt/boxed_region.cpp b/src/rt/boxed_region.cpp
index 2612d0f47b9a..247424088d6b 100644
--- a/src/rt/boxed_region.cpp
+++ b/src/rt/boxed_region.cpp
@@ -1,8 +1,7 @@
-
-
 #include "boxed_region.h"
 #include "rust_globals.h"
 #include "rust_task.h"
+#include "rust_env.h"
 
 // #define DUMP_BOXED_REGION
 
@@ -52,8 +51,15 @@ void boxed_region::free(rust_opaque_box *box) {
     if (box->prev) box->prev->next = box->next;
     if (box->next) box->next->prev = box->prev;
     if (live_allocs == box) live_allocs = box->next;
+
+    if (env->poison_on_free) {
+        memset(box_body(box), 0xab, box->td->size);
+        return;
+    }
+
     box->prev = NULL;
     box->next = NULL;
     box->td = NULL;
+
     backing_region->free(box);
 }
diff --git a/src/rt/boxed_region.h b/src/rt/boxed_region.h
index bd5312fee99f..a3a90f9b7d66 100644
--- a/src/rt/boxed_region.h
+++ b/src/rt/boxed_region.h
@@ -6,6 +6,7 @@
 struct type_desc;
 class memory_region;
 struct rust_opaque_box;
+struct rust_env;
 
 /* Tracks the data allocated by a particular task in the '@' region.
  * Currently still relies on the standard malloc as a backing allocator, but
@@ -13,6 +14,7 @@ struct rust_opaque_box;
  * a type descr which describes the payload (what follows the header). */
 class boxed_region {
 private:
+    rust_env *env;
     memory_region *backing_region;
     rust_opaque_box *live_allocs;
 
@@ -24,8 +26,9 @@ private:
     }
 
 public:
-    boxed_region(memory_region *br)
-        : backing_region(br)
+    boxed_region(rust_env *e, memory_region *br)
+        : env(e)
+        , backing_region(br)
         , live_allocs(NULL)
     {}
 
diff --git a/src/rt/rust_task.cpp b/src/rt/rust_task.cpp
index 20727dbcbfd0..d7c62780fbb1 100644
--- a/src/rt/rust_task.cpp
+++ b/src/rt/rust_task.cpp
@@ -27,7 +27,7 @@ rust_task::rust_task(rust_sched_loop *sched_loop, rust_task_state state,
     list_index(-1),
     rendezvous_ptr(0),
     local_region(&sched_loop->local_region),
-    boxed(&local_region),
+    boxed(sched_loop->kernel->env, &local_region),
     unwinding(false),
     propagate_failure(true),
     cc_counter(0),
diff --git a/src/rustc/driver/session.rs b/src/rustc/driver/session.rs
index 2e9dffb1c2cd..99c6d1ab11e1 100644
--- a/src/rustc/driver/session.rs
+++ b/src/rustc/driver/session.rs
@@ -48,7 +48,10 @@ type options =
      no_trans: bool,
      no_asm_comments: bool,
      debug_rustc: bool,
-     borrowck: uint}; // 0=off,1=warn,2=err
+
+     // temporary hack: 0=off,1=warn,2=err --> if 2, alias is disabled
+     borrowck: uint,
+    };
 
 type crate_metadata = {name: str, data: [u8]};
 
diff --git a/src/rustc/middle/alias.rs b/src/rustc/middle/alias.rs
index 81f90c8eef2e..471e68137e82 100644
--- a/src/rustc/middle/alias.rs
+++ b/src/rustc/middle/alias.rs
@@ -159,6 +159,12 @@ fn visit_block(cx: @ctx, b: ast::blk, sc: scope, v: vt<scope>) {
 }
 
 fn cant_copy(cx: ctx, b: binding) -> bool {
+
+    if cx.tcx.sess.opts.borrowck == 2u {
+        // borrowck is enabled. disable alias analysis.
+        ret false;
+    }
+
     alt b.copied {
       not_allowed { ret true; }
       copied { ret false; }