diff --git a/titans_pytorch/mac_transformer.py b/titans_pytorch/mac_transformer.py
index b97d606..5651108 100644
--- a/titans_pytorch/mac_transformer.py
+++ b/titans_pytorch/mac_transformer.py
@@ -83,6 +83,14 @@ def identity(t):
 def round_up_multiple(seq, mult):
     return ceil(seq / mult) * mult
 
+def pack_with_inverse(t, pattern):
+    packed, packed_shape = pack(t, pattern)
+
+    def inverse(out, inv_pattern = None):
+        return unpack(out, packed_shape, default(inv_pattern, pattern))
+
+    return packed, inverse
+
 def pad_at_dim(t, pad, dim = -1, value = 0.):
     dims_from_right = (- dim - 1) if dim < 0 else (t.ndim - dim - 1)
     zeros = ((0, 0) * dims_from_right)
@@ -576,7 +584,7 @@ def forward(
         x, inverse_segment = pad_and_segment_with_inverse(x, segment_len)
 
         mems = repeat(self.longterm_mems, 'n d -> b n d', b = x.shape[0])
-        x, mem_ps = pack((x, mems), 'b * d')
+        x, inverse_pack_mems = pack_with_inverse((x, mems), 'b * d')
 
         x = inverse_segment(x)
 
@@ -634,7 +642,7 @@ def forward(
 
         x, inverse_segment = pad_and_segment_with_inverse(x, segment_len + num_longterm_mem_tokens)
 
-        x, _ = unpack(x, mem_ps, 'b * d')
+        x, _ = inverse_pack_mems(x)
 
         x = inverse_segment(x)