diff --git a/shape.c b/shape.c
index e264e7bee5..cf1a4426eb 100644
--- a/shape.c
+++ b/shape.c
@@ -145,6 +145,7 @@ get_next_shape_internal(rb_shape_t * shape, ID id, enum shape_type shape_type, b
 
                 new_shape->type = (uint8_t)shape_type;
                 new_shape->capacity = shape->capacity;
+                new_shape->edges = NULL;
 
                 switch (shape_type) {
                   case SHAPE_IVAR:
diff --git a/shape.h b/shape.h
index b635ddf8b7..5366631f8d 100644
--- a/shape.h
+++ b/shape.h
@@ -28,12 +28,12 @@ typedef uint16_t shape_id_t;
 
 # define SHAPE_FLAG_SHIFT ((SIZEOF_VALUE * 8) - SHAPE_ID_NUM_BITS)
 
-# define SHAPE_BITMAP_SIZE 16384
+# define SHAPE_BUFFER_SIZE 0x80000
 
 # define SHAPE_MAX_VARIATIONS 8
 # define SHAPE_MAX_NUM_IVS 80
 
-# define MAX_SHAPE_ID (SHAPE_MASK - 1)
+# define MAX_SHAPE_ID SHAPE_BUFFER_SIZE
 # define INVALID_SHAPE_ID SHAPE_MASK
 # define ROOT_SHAPE_ID 0x0
 
diff --git a/vm.c b/vm.c
index 959966f562..11fc54095b 100644
--- a/vm.c
+++ b/vm.c
@@ -4022,13 +4022,13 @@ Init_vm_objects(void)
 #endif
 
 #ifdef HAVE_MMAP
-    vm->shape_list = (rb_shape_t *)mmap(NULL, rb_size_mul_or_raise(SHAPE_BITMAP_SIZE * 32, sizeof(rb_shape_t), rb_eRuntimeError),
+    vm->shape_list = (rb_shape_t *)mmap(NULL, rb_size_mul_or_raise(SHAPE_BUFFER_SIZE, sizeof(rb_shape_t), rb_eRuntimeError),
                          PROT_READ | PROT_WRITE, MAP_PRIVATE | MAP_ANONYMOUS, -1, 0);
     if (vm->shape_list == MAP_FAILED) {
         vm->shape_list = 0;
     }
 #else
-    vm->shape_list = xcalloc(SHAPE_BITMAP_SIZE * 32, sizeof(rb_shape_t));
+    vm->shape_list = xcalloc(SHAPE_BUFFER_SIZE, sizeof(rb_shape_t));
 #endif
 
     if (!vm->shape_list) {