diff --git a/codex/blocktype.nim b/codex/blocktype.nim
index c27c3d51..d215d169 100644
--- a/codex/blocktype.nim
+++ b/codex/blocktype.nim
@@ -31,7 +31,7 @@ import ./codextypes
 export errors, logutils, units, codextypes
 
 type
-  Block* = object
+  Block* = ref object
     cid*: Cid
     data*: seq[byte]
 
diff --git a/codex/manifest/manifest.nim b/codex/manifest/manifest.nim
index 0ccf5a3d..9aa520e9 100644
--- a/codex/manifest/manifest.nim
+++ b/codex/manifest/manifest.nim
@@ -29,7 +29,7 @@ import ../logutils
 # TODO: Manifest should be reworked to more concrete types,
 # perhaps using inheritance
 type
-  Manifest* = object
+  Manifest* = ref object
     treeCid {.serialize.}: Cid              # Root of the merkle tree
     datasetSize {.serialize.}: NBytes       # Total size of all blocks
     blockSize {.serialize.}: NBytes         # Size of each contained block (might not be needed if blocks are len-prefixed)