diff --git a/src/blockindexworkcomparator.h b/src/blockindexworkcomparator.h
new file mode 100644
--- /dev/null
+++ b/src/blockindexworkcomparator.h
@@ -0,0 +1,43 @@
+// Copyright (c) 2018 The Bitcoin developers
+// Distributed under the MIT software license, see the accompanying
+// file COPYING or http://www.opensource.org/licenses/mit-license.php.
+
+#ifndef BITCOIN_BLOCK_INDEX_WORK_COMPARATOR_H
+#define BITCOIN_BLOCK_INDEX_WORK_COMPARATOR_H
+
+// TODO: Split chain.h apart and only include CBlockIndex
+#include "chain.h"
+
+struct CBlockIndexWorkComparator {
+    bool operator()(const CBlockIndex *pa, const CBlockIndex *pb) const {
+        // First sort by most total work, ...
+        if (pa->nChainWork > pb->nChainWork) {
+            return false;
+        }
+        if (pa->nChainWork < pb->nChainWork) {
+            return true;
+        }
+
+        // ... then by earliest time received, ...
+        if (pa->nSequenceId < pb->nSequenceId) {
+            return false;
+        }
+        if (pa->nSequenceId > pb->nSequenceId) {
+            return true;
+        }
+
+        // Use pointer address as tie breaker (should only happen with blocks
+        // loaded from disk, as those all have id 0).
+        if (pa < pb) {
+            return false;
+        }
+        if (pa > pb) {
+            return true;
+        }
+
+        // Identical blocks.
+        return false;
+    }
+};
+
+#endif // BITCOIN_BLOCK_INDEX_WORK_COMPARATOR_H
diff --git a/src/validation.cpp b/src/validation.cpp
--- a/src/validation.cpp
+++ b/src/validation.cpp
@@ -7,6 +7,7 @@
 #include "validation.h"
 
 #include "arith_uint256.h"
+#include "blockindexworkcomparator.h"
 #include "chainparams.h"
 #include "checkpoints.h"
 #include "checkqueue.h"
@@ -94,38 +95,6 @@
 // Internal stuff
 namespace {
 
-struct CBlockIndexWorkComparator {
-    bool operator()(const CBlockIndex *pa, const CBlockIndex *pb) const {
-        // First sort by most total work, ...
-        if (pa->nChainWork > pb->nChainWork) {
-            return false;
-        }
-        if (pa->nChainWork < pb->nChainWork) {
-            return true;
-        }
-
-        // ... then by earliest time received, ...
-        if (pa->nSequenceId < pb->nSequenceId) {
-            return false;
-        }
-        if (pa->nSequenceId > pb->nSequenceId) {
-            return true;
-        }
-
-        // Use pointer address as tie breaker (should only happen with blocks
-        // loaded from disk, as those all have id 0).
-        if (pa < pb) {
-            return false;
-        }
-        if (pa > pb) {
-            return true;
-        }
-
-        // Identical blocks.
-        return false;
-    }
-};
-
 CBlockIndex *pindexBestInvalid;
 
 /**