gistfile1.txt

diff --git a/src/core/frame.c b/src/core/frame.c
index 162e8c0..763d473 100644
--- a/src/core/frame.c
+++ b/src/core/frame.c
@@ -946,6 +946,8 @@ void MVM_frame_unwind_to(MVMThreadContext *tc, MVMFrame *frame, MVMuint8 *abs_ad
             cur_frame->mark_special_return_data = mark_unwind_data;
             {
                 MVMUnwindData *ud = MVM_malloc(sizeof(MVMUnwindData));
+if (MVM_FRAME_IS_ON_CALLSTACK(tc, frame))
+    MVM_panic(1, "Stacked frame!!");
                 ud->frame = frame;
                 ud->abs_addr = abs_addr;
                 ud->rel_addr = rel_addr;
diff --git a/src/gc/wb.h b/src/gc/wb.h
index 92a3c24..9a0616d 100644
--- a/src/gc/wb.h
+++ b/src/gc/wb.h
@@ -16,6 +16,8 @@ MVM_STATIC_INLINE void MVM_gc_write_barrier(MVMThreadContext *tc, MVMCollectable
 #define MVM_ASSIGN_REF(tc, update_root, update_addr, referenced) \
     { \
         void *_r = referenced; \
+        if (_r && ((MVMCollectable *)_r)->owner == 0) \
+            MVM_panic(1, "Invalid assignment (maybe of heap frame to stack frame?)"); \
         MVM_gc_write_barrier(tc, update_root, (MVMCollectable *)_r); \
         update_addr = _r; \
     }