diff --git a/src/node/blockstorage.cpp b/src/node/blockstorage.cpp
index 57f81e6bb6a..9fea644f05c 100644
--- a/src/node/blockstorage.cpp
+++ b/src/node/blockstorage.cpp
@@ -524,6 +524,16 @@ void BlockManager::FlushUndoFile(int block_file, bool finalize)
 void BlockManager::FlushBlockFile(bool fFinalize, bool finalize_undo)
 {
     LOCK(cs_LastBlockFile);
+
+    if (m_blockfile_info.size() < 1) {
+        // Return if we haven't loaded any blockfiles yet. This happens during
+        // chainstate init, when we call ChainstateManager::MaybeRebalanceCaches() (which
+        // then calls FlushStateToDisk()), resulting in a call to this function before we
+        // have populated `m_blockfile_info` via LoadBlockIndexDB().
+        return;
+    }
+    assert(static_cast<int>(m_blockfile_info.size()) > m_last_blockfile);
+
     FlatFilePos block_pos_old(m_last_blockfile, m_blockfile_info[m_last_blockfile].nSize);
     if (!BlockFileSeq().Flush(block_pos_old, fFinalize)) {
         AbortNode("Flushing block file to disk failed. This is likely the result of an I/O error.");