diff --git a/codex/slotbuilder/slotbuilder.nim b/codex/slotbuilder/slotbuilder.nim
index cc912b1b..12be8267 100644
--- a/codex/slotbuilder/slotbuilder.nim
+++ b/codex/slotbuilder/slotbuilder.nim
@@ -30,7 +30,10 @@ proc new*(
     return failure("Can only create SlotBuilder using protected manifests.")
 
   if (manifest.blocksCount mod manifest.ecK) != 0:
-    return failure("Number of blocks must be devisable by number of slots.")
+    return failure("Number of blocks must be divisable by number of slots.")
+
+  if (manifest.blockSize.int mod CellSize) != 0:
+    return failure("Block size must be divisable by cell size.")
 
   let numberOfSlotBlocks = manifest.blocksCount div manifest.ecK
   success(SlotBuilder(
diff --git a/tests/codex/slotbuilder/testslotbuilder.nim b/tests/codex/slotbuilder/testslotbuilder.nim
index 45018a84..8319517f 100644
--- a/tests/codex/slotbuilder/testslotbuilder.nim
+++ b/tests/codex/slotbuilder/testslotbuilder.nim
@@ -96,6 +96,21 @@ asyncchecksuite "Slot builder":
     check:
       SlotBuilder.new(localStore, mismatchManifest).isErr
 
+  test "Block size must be divisable by cell size":
+    let mismatchManifest = Manifest.new(
+      manifest = Manifest.new(
+        treeCid = Cid.example,
+        blockSize = (blockSize - 1).NBytes,
+        datasetSize = (datasetSize - numberOfDatasetBlocks).NBytes),
+      treeCid = Cid.example,
+      datasetSize = (datasetSize - numberOfDatasetBlocks).NBytes,
+      ecK = numberOfSlots,
+      ecM = 0
+    )
+
+    check:
+      SlotBuilder.new(localStore, mismatchManifest).isErr
+
   proc getNextPowerOfTwo(i: int): int =
     if i < 1:
       return 1
@@ -178,5 +193,3 @@ asyncchecksuite "Slot builder":
       # 1 pad block
       slotTree.getLeafCid(numberOfSlotBlocks).tryget() == expectedEmptyCid
 
-
-