diff --git a/bin/wasm-node/CHANGELOG.md b/bin/wasm-node/CHANGELOG.md
index 1ad323b08a..b9feba2265 100644
--- a/bin/wasm-node/CHANGELOG.md
+++ b/bin/wasm-node/CHANGELOG.md
@@ -5,6 +5,7 @@
 ### Fixed
 
 - Syncing no longer stalls if the gap between the finalized and latest block is more than 100 blocks. ([#2801](https://github.com/paritytech/smoldot/pull/2801))
+- No longer silently discard justifications when receive a block from the network that was already known locally. ([#2800](https://github.com/paritytech/smoldot/pull/2800))
 - CPU-heavy operations such as verifying finality proofs or compiling the runtime will now better respect the CPU rate limit. ([#2803](https://github.com/paritytech/smoldot/pull/2803))
 
 ## 0.7.0 - 2022-09-28
diff --git a/src/sync/all_forks.rs b/src/sync/all_forks.rs
index d8b3bf2e5b..2be33a6f7a 100644
--- a/src/sync/all_forks.rs
+++ b/src/sync/all_forks.rs
@@ -1129,6 +1129,12 @@ impl<TBl, TRq, TSrc> FinishAncestrySearch<TBl, TRq, TSrc> {
             return Err((AncestrySearchResponseError::TooOld, self.finish()));
         }
 
+        // Convert the justifications in an "owned" format, because we're likely going to store
+        // them.
+        let justifications = scale_encoded_justifications
+            .map(|(e, j)| (e, j.as_ref().to_owned()))
+            .collect::<Vec<_>>();
+
         // If the block is already part of the local tree of blocks, nothing more to do.
         if self
             .inner
@@ -1139,6 +1145,7 @@ impl<TBl, TRq, TSrc> FinishAncestrySearch<TBl, TRq, TSrc> {
                 inner: self,
                 decoded_header: decoded_header.into(),
                 is_verified: true,
+                justifications,
             }));
         }
 
@@ -1171,15 +1178,14 @@ impl<TBl, TRq, TSrc> FinishAncestrySearch<TBl, TRq, TSrc> {
             Ok(AddBlock::UnknownBlock(AddBlockVacant {
                 inner: self,
                 decoded_header: decoded_header.into(),
-                justifications: scale_encoded_justifications
-                    .map(|(e, j)| (e, j.as_ref().to_owned()))
-                    .collect::<Vec<_>>(),
+                justifications,
             }))
         } else {
             Ok(AddBlock::AlreadyPending(AddBlockOccupied {
                 inner: self,
                 decoded_header: decoded_header.into(),
                 is_verified: false,
+                justifications,
             }))
         }
     }
@@ -1231,6 +1237,7 @@ pub struct AddBlockOccupied<TBl, TRq, TSrc> {
     inner: FinishAncestrySearch<TBl, TRq, TSrc>,
     decoded_header: header::Header,
     is_verified: bool,
+    justifications: Vec<([u8; 4], Vec<u8>)>,
 }
 
 impl<TBl, TRq, TSrc> AddBlockOccupied<TBl, TRq, TSrc> {
@@ -1319,9 +1326,14 @@ impl<TBl, TRq, TSrc> AddBlockOccupied<TBl, TRq, TSrc> {
             mem::replace(&mut block_user_data.user_data, user_data)
         };
 
-        // TODO: what if the pending block already contains a justification and it is not the
-        //       same as here? since justifications aren't immediately verified, it is possible
-        //       for a malicious peer to send us bad justifications
+        if !self.justifications.is_empty() {
+            self.inner.inner.inner.blocks[self.inner.source_id]
+                .unverified_finality_proofs
+                .insert(
+                    self.decoded_header.number,
+                    FinalityProofs::Justifications(self.justifications),
+                );
+        }
 
         // Update the state machine for the next iteration.
         // Note: this can't be reached if `expected_next_height` is 0, because that should have