diff --git a/chain-impl-mockchain/src/block/mod.rs b/chain-impl-mockchain/src/block/mod.rs
index 73e33a487..46625cf6e 100644
--- a/chain-impl-mockchain/src/block/mod.rs
+++ b/chain-impl-mockchain/src/block/mod.rs
@@ -145,15 +145,16 @@ impl Readable for Block {
         let mut contents = ContentsBuilder::new();
 
         while remaining_content_size > 0 {
-            let message_size = buf.get_u16()?;
-            let mut message_buf = buf.split_to(message_size as usize)?;
+            let message_raw = FragmentRaw::read(buf)?;
+            let message_size = message_raw.size_bytes_plus_size();
 
             // return error here if message serialize sized is bigger than remaining size
 
-            let message = Fragment::read(&mut message_buf)?;
+            let message = Fragment::from_raw(&message_raw)
+                .map_err(|e| ReadError::StructureInvalid(e.to_string()))?;
             contents.push(message);
 
-            remaining_content_size -= 2 + message_size as u32;
+            remaining_content_size -= message_size as u32;
         }
 
         Ok(Block {
diff --git a/chain-impl-mockchain/src/fragment/raw.rs b/chain-impl-mockchain/src/fragment/raw.rs
index 7d046641d..bcbe40ad4 100644
--- a/chain-impl-mockchain/src/fragment/raw.rs
+++ b/chain-impl-mockchain/src/fragment/raw.rs
@@ -1,7 +1,9 @@
 use crate::key::Hash;
 use chain_core::property;
+use chain_ser::mempack::{ReadBuf, ReadError, Readable};
 
 pub type FragmentId = Hash;
+pub const FRAGMENT_SIZE_BYTES_LEN: usize = 4;
 
 /// A serialized Message
 #[derive(Debug, Clone, PartialEq, Eq)]
@@ -9,7 +11,7 @@ pub struct FragmentRaw(pub(super) Vec<u8>);
 
 impl FragmentRaw {
     pub fn size_bytes_plus_size(&self) -> usize {
-        2 + self.0.len()
+        FRAGMENT_SIZE_BYTES_LEN + self.0.len()
     }
 
     pub fn id(&self) -> FragmentId {
@@ -23,12 +25,21 @@ impl AsRef<[u8]> for FragmentRaw {
     }
 }
 
+impl Readable for FragmentRaw {
+    fn read(buf: &mut ReadBuf) -> Result<Self, ReadError> {
+        let size = buf.get_u32()?;
+        let mut v = vec![0u8; size as usize];
+        buf.copy_to_slice_mut(&mut v)?;
+        Ok(FragmentRaw(v))
+    }
+}
+
 impl property::Deserialize for FragmentRaw {
     type Error = std::io::Error;
     fn deserialize<R: std::io::BufRead>(reader: R) -> Result<Self, Self::Error> {
         use chain_core::packer::*;
         let mut codec = Codec::new(reader);
-        let size = codec.get_u16()?;
+        let size = codec.get_u32()?;
         let mut v = vec![0u8; size as usize];
         codec.into_inner().read_exact(&mut v)?;
         Ok(FragmentRaw(v))
@@ -41,7 +52,7 @@ impl property::Serialize for FragmentRaw {
         use chain_core::packer::*;
 
         let mut codec = Codec::new(writer);
-        codec.put_u16(self.0.len() as u16)?;
+        codec.put_u32(self.0.len() as u32)?;
         codec.into_inner().write_all(&self.0)?;
         Ok(())
     }
diff --git a/chain-impl-mockchain/src/fragment/test.rs b/chain-impl-mockchain/src/fragment/test.rs
index 85afd79e2..49f5368b6 100644
--- a/chain-impl-mockchain/src/fragment/test.rs
+++ b/chain-impl-mockchain/src/fragment/test.rs
@@ -1,7 +1,7 @@
 use super::*;
 use crate::config::ConfigParam;
 #[cfg(test)]
-use crate::testing::serialization::serialization_bijection_r;
+use crate::testing::serialization::{serialization_bijection, serialization_bijection_r};
 #[cfg(test)]
 use quickcheck::TestResult;
 use quickcheck::{Arbitrary, Gen};
@@ -30,11 +30,16 @@ impl Arbitrary for Fragment {
 }
 
 #[quickcheck]
-fn fragment_serialization_bijection(b: Fragment) -> TestResult {
+fn fragment_raw_bijection(b: Fragment) -> TestResult {
     let b_got = Fragment::from_raw(&b.to_raw()).unwrap();
     TestResult::from_bool(b == b_got)
 }
 
+#[quickcheck]
+fn fragment_serialization_bijection(b: Fragment) -> TestResult {
+    serialization_bijection(b)
+}
+
 quickcheck! {
     fn initial_ents_serialization_bijection(config_params: ConfigParams) -> TestResult {
         serialization_bijection_r(config_params)