diff --git a/src/validation.h b/src/validation.h
--- a/src/validation.h
+++ b/src/validation.h
@@ -637,7 +637,7 @@
                            BlockValidationState &state, CBlockIndex **ppindex)
         EXCLUSIVE_LOCKS_REQUIRED(cs_main);
 
-    CBlockIndex *LookupBlockIndex(const BlockHash &hash)
+    CBlockIndex *LookupBlockIndex(const BlockHash &hash) const
         EXCLUSIVE_LOCKS_REQUIRED(cs_main);
 
     /** Find the last common block between the parameter chain and a locator. */
diff --git a/src/validation.cpp b/src/validation.cpp
--- a/src/validation.cpp
+++ b/src/validation.cpp
@@ -149,7 +149,7 @@
     : excessiveBlockSize(config.GetMaxBlockSize()), checkPoW(true),
       checkMerkleRoot(true) {}
 
-CBlockIndex *BlockManager::LookupBlockIndex(const BlockHash &hash) {
+CBlockIndex *BlockManager::LookupBlockIndex(const BlockHash &hash) const {
     AssertLockHeld(cs_main);
     assert(std::addressof(g_chainman.BlockIndex()) ==
            std::addressof(m_block_index));