diff --git a/src/wallet/wallet.cpp b/src/wallet/wallet.cpp
index ade460d6a..65defc30a 100644
--- a/src/wallet/wallet.cpp
+++ b/src/wallet/wallet.cpp
@@ -846,14 +846,19 @@ void CWallet::MarkConflicted(const uint256& hashBlock, const uint256& hashTx)
 {
     LOCK2(cs_main, cs_wallet);
 
-    CBlockIndex* pindex;
-    assert(mapBlockIndex.count(hashBlock));
-    pindex = mapBlockIndex[hashBlock];
     int conflictconfirms = 0;
-    if (chainActive.Contains(pindex)) {
-        conflictconfirms = -(chainActive.Height() - pindex->nHeight + 1);
+    if (mapBlockIndex.count(hashBlock)) {
+        CBlockIndex* pindex = mapBlockIndex[hashBlock];
+        if (chainActive.Contains(pindex)) {
+            conflictconfirms = -(chainActive.Height() - pindex->nHeight + 1);
+        }
     }
-    assert(conflictconfirms < 0);
+    // If number of conflict confirms cannot be determined, this means
+    // that the block is still unknown or not yet part of the main chain,
+    // for example when loading the wallet during a reindex. Do nothing in that
+    // case.
+    if (conflictconfirms >= 0)
+        return;
 
     // Do not flush the wallet here for performance reasons
     CWalletDB walletdb(strWalletFile, "r+", false);