diff --git a/shape.h b/shape.h
index c634055cb6..b3e4927f57 100644
--- a/shape.h
+++ b/shape.h
@@ -20,7 +20,7 @@ STATIC_ASSERT(shape_id_num_bits, SHAPE_ID_NUM_BITS == sizeof(shape_id_t) * CHAR_
 #define SHAPE_ID_FL_NON_CANONICAL_MASK (SHAPE_FL_NON_CANONICAL_MASK << SHAPE_ID_OFFSET_NUM_BITS)
 
 #define SHAPE_ID_HEAP_INDEX_BITS 3
-#define SHAPE_ID_HEAP_INDEX_OFFSET (SHAPE_ID_NUM_BITS - SHAPE_ID_HEAP_INDEX_BITS)
+#define SHAPE_ID_HEAP_INDEX_OFFSET (SHAPE_ID_NUM_BITS - SHAPE_ID_HEAP_INDEX_BITS - 1) // FIXME: -1 to avoid crashing YJIT
 #define SHAPE_ID_HEAP_INDEX_MAX ((1 << SHAPE_ID_HEAP_INDEX_BITS) - 1)
 #define SHAPE_ID_HEAP_INDEX_MASK (SHAPE_ID_HEAP_INDEX_MAX << SHAPE_ID_HEAP_INDEX_OFFSET)