diff --git a/src/chain.h b/src/chain.h
--- a/src/chain.h
+++ b/src/chain.h
@@ -13,6 +13,7 @@
 #include "tinyformat.h"
 #include "uint256.h"
 
+#include <unordered_map>
 #include <vector>
 
 class CBlockFileInfo {
@@ -353,6 +354,16 @@
     const CBlockIndex *GetAncestor(int height) const;
 };
 
+/**
+ * Maintain a map of CBlockIndex for all known headers.
+ */
+struct BlockHasher {
+    size_t operator()(const uint256 &hash) const { return hash.GetCheapHash(); }
+};
+
+typedef std::unordered_map<uint256, CBlockIndex *, BlockHasher> BlockMap;
+extern BlockMap mapBlockIndex;
+
 arith_uint256 GetBlockProof(const CBlockIndex &block);
 
 /**
diff --git a/src/checkpoints.cpp b/src/checkpoints.cpp
--- a/src/checkpoints.cpp
+++ b/src/checkpoints.cpp
@@ -6,8 +6,6 @@
 
 #include "chain.h"
 #include "chainparams.h"
-#include "uint256.h"
-#include "validation.h"
 
 #include <cstdint>
 
@@ -22,8 +20,11 @@
          boost::adaptors::reverse(checkpoints)) {
         const uint256 &hash = i.second;
         BlockMap::const_iterator t = mapBlockIndex.find(hash);
-        if (t != mapBlockIndex.end()) return t->second;
+        if (t != mapBlockIndex.end()) {
+            return t->second;
+        }
     }
+
     return nullptr;
 }
 
diff --git a/src/validation.h b/src/validation.h
--- a/src/validation.h
+++ b/src/validation.h
@@ -20,6 +20,7 @@
 #include "versionbits.h"
 
 #include <algorithm>
+#include <atomic>
 #include <cstdint>
 #include <exception>
 #include <map>
@@ -28,10 +29,7 @@
 #include <utility>
 #include <vector>
 
-#include <atomic>
-
 #include <boost/filesystem/path.hpp>
-#include <unordered_map>
 
 class CBlockIndex;
 class CBlockTreeDB;
@@ -167,15 +165,9 @@
 
 static const bool DEFAULT_PEERBLOOMFILTERS = true;
 
-struct BlockHasher {
-    size_t operator()(const uint256 &hash) const { return hash.GetCheapHash(); }
-};
-
 extern CScript COINBASE_FLAGS;
 extern CCriticalSection cs_main;
 extern CTxMemPool mempool;
-typedef std::unordered_map<uint256, CBlockIndex *, BlockHasher> BlockMap;
-extern BlockMap mapBlockIndex;
 extern uint64_t nLastBlockTx;
 extern uint64_t nLastBlockSize;
 extern const std::string strMessageMagic;