diff --git a/src/main.cpp b/src/main.cpp
index 9295c81ce8..172d43c658 100644
--- a/src/main.cpp
+++ b/src/main.cpp
@@ -2362,8 +2362,11 @@ bool FindBlockPos(CValidationState &state, CDiskBlockPos &pos, unsigned int nAdd
     }
 
     nLastBlockFile = nFile;
-    vinfoBlockFile[nFile].nSize += nAddSize;
     vinfoBlockFile[nFile].AddBlock(nHeight, nTime);
+    if (fKnown)
+        vinfoBlockFile[nFile].nSize = std::max(pos.nPos + nAddSize, vinfoBlockFile[nFile].nSize);
+    else
+        vinfoBlockFile[nFile].nSize += nAddSize;
 
     if (!fKnown) {
         unsigned int nOldChunks = (pos.nPos + BLOCKFILE_CHUNK_SIZE - 1) / BLOCKFILE_CHUNK_SIZE;