diff --git a/src/main.cpp b/src/main.cpp
index 6eff7c921..cb4ffed18 100644
--- a/src/main.cpp
+++ b/src/main.cpp
@@ -1613,7 +1613,7 @@ bool ReadBlockFromDisk(int32_t height,CBlock& block, const CDiskBlockPos& pos)
     if (!(CheckEquihashSolution(&block, Params()) && CheckProofOfWork(height,pubkey33,block.GetHash(), block.nBits, Params().GetConsensus())))
     {
         int32_t i; for (i=0; i<33; i++)
-            printf("%02x",pubkey33[i]);
+            fprintf(stderr,"%02x",pubkey33[i]);
         fprintf(stderr," warning unexpected diff at ht.%d\n",height);
         
         return error("ReadBlockFromDisk: Errors in block header at %s", pos.ToString());