diff --git a/src/avalanche/processor.cpp b/src/avalanche/processor.cpp
--- a/src/avalanche/processor.cpp
+++ b/src/avalanche/processor.cpp
@@ -544,7 +544,9 @@
     return hasher.GetHash();
 }
 
-uint256 Processor::buildRemoteSighash(CNode *pfrom) const {
+uint256 Processor::buildRemoteSighash(CNode *pfrom) const
+    EXCLUSIVE_LOCKS_REQUIRED(pfrom->cs_avalanche_state) {
+    AssertLockHeld(pfrom->cs_avalanche_state);
     CHashWriter hasher(SER_GETHASH, 0);
     hasher << pfrom->m_avalanche_state->delegation.getId();
     hasher << pfrom->nRemoteHostNonce;
diff --git a/src/net.h b/src/net.h
--- a/src/net.h
+++ b/src/net.h
@@ -1010,6 +1010,7 @@
     // m_proof_relay == nullptr if we're not relaying proofs with this peer
     std::unique_ptr<ProofRelay> m_proof_relay;
 
+    Mutex cs_avalanche_state;
     struct AvalancheState {
         AvalancheState() {}
 
@@ -1017,7 +1018,8 @@
     };
 
     // m_avalanche_state == nullptr if we're not using avalanche with this peer
-    std::unique_ptr<AvalancheState> m_avalanche_state;
+    std::unique_ptr<AvalancheState>
+        m_avalanche_state GUARDED_BY(cs_avalanche_state);
 
     // Used for headers announcements - unfiltered blocks to relay
     std::vector<BlockHash> vBlockHashesToAnnounce GUARDED_BY(cs_inventory);
diff --git a/src/net_processing.cpp b/src/net_processing.cpp
--- a/src/net_processing.cpp
+++ b/src/net_processing.cpp
@@ -4118,6 +4118,8 @@
     }
 
     if (msg_type == NetMsgType::AVAHELLO) {
+        LOCK(pfrom.cs_avalanche_state);
+
         if (!pfrom.m_avalanche_state) {
             pfrom.m_avalanche_state = std::make_unique<CNode::AvalancheState>();
         }