diff --git a/src/chain.cpp b/src/chain.cpp
index 9f40c41fd..7ebc08a50 100644
--- a/src/chain.cpp
+++ b/src/chain.cpp
@@ -80,12 +80,13 @@ int static inline GetSkipHeight(int height) {
     return (height & 1) ? InvertLowestOne(InvertLowestOne(height - 1)) + 1 : InvertLowestOne(height);
 }
 
-CBlockIndex* CBlockIndex::GetAncestor(int height)
+const CBlockIndex* CBlockIndex::GetAncestor(int height) const
 {
-    if (height > nHeight || height < 0)
+    if (height > nHeight || height < 0) {
         return nullptr;
+    }
 
-    CBlockIndex* pindexWalk = this;
+    const CBlockIndex* pindexWalk = this;
     int heightWalk = nHeight;
     while (heightWalk > height) {
         int heightSkip = GetSkipHeight(heightWalk);
@@ -106,9 +107,9 @@ CBlockIndex* CBlockIndex::GetAncestor(int height)
     return pindexWalk;
 }
 
-const CBlockIndex* CBlockIndex::GetAncestor(int height) const
+CBlockIndex* CBlockIndex::GetAncestor(int height)
 {
-    return const_cast<CBlockIndex*>(this)->GetAncestor(height);
+    return const_cast<CBlockIndex*>(static_cast<const CBlockIndex*>(this)->GetAncestor(height));
 }
 
 void CBlockIndex::BuildSkip()