diff --git a/src/miner.h b/src/miner.h
index bf79bdfd6..cc9c62c1f 100644
--- a/src/miner.h
+++ b/src/miner.h
@@ -71,7 +71,7 @@ struct modifiedentry_iter {
 // TODO: refactor to avoid duplication of this logic.
 struct CompareModifiedEntry {
     bool operator()(const CTxMemPoolModifiedEntry &a,
-                    const CTxMemPoolModifiedEntry &b) {
+                    const CTxMemPoolModifiedEntry &b) const {
         double f1 = double(b.nSizeWithAncestors *
                            a.nModFeesWithAncestors.GetSatoshis());
         double f2 = double(a.nSizeWithAncestors *
@@ -87,7 +87,7 @@ 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();
         return CTxMemPool::CompareIteratorByHash()(a, b);
diff --git a/src/txmempool.h b/src/txmempool.h
index c51ca831b..72c066335 100644
--- a/src/txmempool.h
+++ b/src/txmempool.h
@@ -245,7 +245,7 @@ struct mempoolentry_txid {
  */
 class CompareTxMemPoolEntryByDescendantScore {
 public:
-    bool operator()(const CTxMemPoolEntry &a, const CTxMemPoolEntry &b) {
+    bool operator()(const CTxMemPoolEntry &a, const CTxMemPoolEntry &b) const {
         bool fUseADescendants = UseDescendantScore(a);
         bool fUseBDescendants = UseDescendantScore(b);
 
@@ -272,7 +272,7 @@ class CompareTxMemPoolEntryByDescendantScore {
     }
 
     // Calculate which score to use for an entry (avoiding division).
-    bool UseDescendantScore(const CTxMemPoolEntry &a) {
+    bool UseDescendantScore(const CTxMemPoolEntry &a) const {
         double f1 = double(a.GetSizeWithDescendants() *
                            a.GetModifiedFee().GetSatoshis());
         double f2 =
@@ -287,7 +287,7 @@ class CompareTxMemPoolEntryByDescendantScore {
  */
 class CompareTxMemPoolEntryByScore {
 public:
-    bool operator()(const CTxMemPoolEntry &a, const CTxMemPoolEntry &b) {
+    bool operator()(const CTxMemPoolEntry &a, const CTxMemPoolEntry &b) const {
         double f1 = double(b.GetTxSize() * a.GetModifiedFee().GetSatoshis());
         double f2 = double(a.GetTxSize() * b.GetModifiedFee().GetSatoshis());
         if (f1 == f2) {
@@ -299,14 +299,14 @@ class CompareTxMemPoolEntryByScore {
 
 class CompareTxMemPoolEntryByEntryTime {
 public:
-    bool operator()(const CTxMemPoolEntry &a, const CTxMemPoolEntry &b) {
+    bool operator()(const CTxMemPoolEntry &a, const CTxMemPoolEntry &b) const {
         return a.GetTime() < b.GetTime();
     }
 };
 
 class CompareTxMemPoolEntryByAncestorFee {
 public:
-    bool operator()(const CTxMemPoolEntry &a, const CTxMemPoolEntry &b) {
+    bool operator()(const CTxMemPoolEntry &a, const CTxMemPoolEntry &b) const {
         double aFees = double(a.GetModFeesWithAncestors().GetSatoshis());
         double aSize = a.GetSizeWithAncestors();