diff --git a/ouroboros-consensus-byron/src/Ouroboros/Consensus/Byron/Ledger/Block.hs b/ouroboros-consensus-byron/src/Ouroboros/Consensus/Byron/Ledger/Block.hs
index dfabdba24eb..97b3dda8712 100644
--- a/ouroboros-consensus-byron/src/Ouroboros/Consensus/Byron/Ledger/Block.hs
+++ b/ouroboros-consensus-byron/src/Ouroboros/Consensus/Byron/Ledger/Block.hs
@@ -153,7 +153,14 @@ instance GetHeader ByronBlock where
             CC.ABOBBoundary blk -> recoverBytes       blk
       }
     where
-      overhead = 5 {- CBOR-in-CBOR -} + 2 {- EBB tag -}
+      -- The maximum block size is 65536, the CBOR-in-CBOR tag for this block
+      -- is:
+      --
+      -- > D8 18          # tag(24)
+      -- >    1A 00010000 # bytes(65536)
+      --
+      -- Which is 7 bytes, enough for up to 4294967295 bytes.
+      overhead = 7 {- CBOR-in-CBOR -} + 2 {- EBB tag -}
 
   -- Check if a block matches its header
   --
diff --git a/ouroboros-consensus-cardano/test/golden/CardanoNodeToNodeVersion2/Header_Byron_EBB b/ouroboros-consensus-cardano/test/golden/CardanoNodeToNodeVersion2/Header_Byron_EBB
index 9b6534973da..f69f3d57969 100644
Binary files a/ouroboros-consensus-cardano/test/golden/CardanoNodeToNodeVersion2/Header_Byron_EBB and b/ouroboros-consensus-cardano/test/golden/CardanoNodeToNodeVersion2/Header_Byron_EBB differ
diff --git a/ouroboros-consensus-cardano/test/golden/CardanoNodeToNodeVersion2/Header_Byron_regular b/ouroboros-consensus-cardano/test/golden/CardanoNodeToNodeVersion2/Header_Byron_regular
index 594c59ad74e..749614e068b 100644
Binary files a/ouroboros-consensus-cardano/test/golden/CardanoNodeToNodeVersion2/Header_Byron_regular and b/ouroboros-consensus-cardano/test/golden/CardanoNodeToNodeVersion2/Header_Byron_regular differ
diff --git a/ouroboros-consensus-shelley/src/Ouroboros/Consensus/Shelley/Node.hs b/ouroboros-consensus-shelley/src/Ouroboros/Consensus/Shelley/Node.hs
index 3cb5ec05a2b..41081fb9025 100644
--- a/ouroboros-consensus-shelley/src/Ouroboros/Consensus/Shelley/Node.hs
+++ b/ouroboros-consensus-shelley/src/Ouroboros/Consensus/Shelley/Node.hs
@@ -374,7 +374,14 @@ instance ConfigSupportsNode (ShelleyBlock c) where
 instance TPraosCrypto c => RunNode (ShelleyBlock c) where
   nodeBlockFetchSize hdr = overhead + headerSize + bodySize
     where
-      overhead   = 5 {- CBOR-in-CBOR -} + 1 {- encodeListLen -}
+      -- The maximum block size is 65536, the CBOR-in-CBOR tag for this block
+      -- is:
+      --
+      -- > D8 18          # tag(24)
+      -- >    1A 00010000 # bytes(65536)
+      --
+      -- Which is 7 bytes, enough for up to 4294967295 bytes.
+      overhead   = 7 {- CBOR-in-CBOR -} + 1 {- encodeListLen -}
       bodySize   = fromIntegral . SL.bsize . SL.bhbody . shelleyHeaderRaw $ hdr
       headerSize = fromIntegral . SL.bHeaderSize . shelleyHeaderRaw $ hdr
 
diff --git a/ouroboros-consensus/ouroboros-consensus-mock/src/Ouroboros/Consensus/Mock/Node.hs b/ouroboros-consensus/ouroboros-consensus-mock/src/Ouroboros/Consensus/Mock/Node.hs
index dc1d5aae2bd..1a0bc103504 100644
--- a/ouroboros-consensus/ouroboros-consensus-mock/src/Ouroboros/Consensus/Mock/Node.hs
+++ b/ouroboros-consensus/ouroboros-consensus-mock/src/Ouroboros/Consensus/Mock/Node.hs
@@ -58,7 +58,7 @@ instance ( LedgerSupportsProtocol      (SimpleBlock SimpleMockCrypto ext)
          , RunMockBlock SimpleMockCrypto ext
          ) => RunNode (SimpleBlock SimpleMockCrypto ext) where
   nodeBlockFetchSize hdr =
-      5 {- CBOR-in-CBOR -} + 1 {- encodeListLen 2 -} + hdrSize + bodySize
+      7 {- CBOR-in-CBOR -} + 1 {- encodeListLen 2 -} + hdrSize + bodySize
     where
       hdrSize  = fromIntegral (Lazy.length (serialise hdr))
       bodySize = simpleBodySize (simpleHeaderStd hdr)