diff --git a/src/miner.h b/src/miner.h
index 57dceba96..927ddae07 100644
--- a/src/miner.h
+++ b/src/miner.h
@@ -73,7 +73,7 @@ struct modifiedentry_iter {
 // except operating on CTxMemPoolModifiedEntry.
 // TODO: refactor to avoid duplication of this logic.
 struct CompareModifiedEntry {
-    bool operator()(const CTxMemPoolModifiedEntry &a, const CTxMemPoolModifiedEntry &b)
+    bool operator()(const CTxMemPoolModifiedEntry &a, const CTxMemPoolModifiedEntry &b) const
     {
         double f1 = (double)a.nModFeesWithAncestors * b.nSizeWithAncestors;
         double f2 = (double)b.nModFeesWithAncestors * a.nSizeWithAncestors;
@@ -88,7 +88,7 @@ struct CompareModifiedEntry {
 // This is sufficient to sort an ancestor package in an order that is valid
 // to appear in a block.
 struct CompareTxIterByAncestorCount {
-    bool operator()(const CTxMemPool::txiter &a, const CTxMemPool::txiter &b)
+    bool operator()(const CTxMemPool::txiter &a, const CTxMemPool::txiter &b) const
     {
         if (a->GetCountWithAncestors() != b->GetCountWithAncestors())
             return a->GetCountWithAncestors() < b->GetCountWithAncestors();
diff --git a/src/txmempool.h b/src/txmempool.h
index 6c1256be1..5448209a7 100644
--- a/src/txmempool.h
+++ b/src/txmempool.h
@@ -283,7 +283,7 @@ public:
 class CompareTxMemPoolEntryByAncestorFee
 {
 public:
-    bool operator()(const CTxMemPoolEntry& a, const CTxMemPoolEntry& b)
+    bool operator()(const CTxMemPoolEntry& a, const CTxMemPoolEntry& b) const
     {
         double aFees = a.GetModFeesWithAncestors();
         double aSize = a.GetSizeWithAncestors();