diff --git a/src/pow.cpp b/src/pow.cpp
index e57fd866f..e06d9662e 100644
--- a/src/pow.cpp
+++ b/src/pow.cpp
@@ -12,12 +12,9 @@
 
 unsigned int GetNextWorkRequired(const CBlockIndex* pindexLast, const CBlockHeader *pblock, const Consensus::Params& params)
 {
+    assert(pindexLast != NULL);
     unsigned int nProofOfWorkLimit = UintToArith256(params.powLimit).GetCompact();
 
-    // Genesis block
-    if (pindexLast == NULL)
-        return nProofOfWorkLimit;
-
     // Only change once per difficulty adjustment interval
     if ((pindexLast->nHeight+1) % params.DifficultyAdjustmentInterval() != 0)
     {
diff --git a/src/validation.cpp b/src/validation.cpp
index 63918a3f3..be82026b3 100644
--- a/src/validation.cpp
+++ b/src/validation.cpp
@@ -1714,7 +1714,10 @@ bool ConnectBlock(const CBlock& block, CValidationState& state, CBlockIndex* pin
                   CCoinsViewCache& view, const CChainParams& chainparams, bool fJustCheck)
 {
     AssertLockHeld(cs_main);
-
+    assert(pindex);
+    // pindex->phashBlock can be null if called by CreateNewBlock/TestBlockValidity
+    assert((pindex->phashBlock == NULL) ||
+           (*pindex->phashBlock == block.GetHash()));
     int64_t nTimeStart = GetTimeMicros();
 
     // Check it again in case a previous version let a bad block in
@@ -2948,7 +2951,8 @@ std::vector<unsigned char> GenerateCoinbaseCommitment(CBlock& block, const CBloc
 
 bool ContextualCheckBlockHeader(const CBlockHeader& block, CValidationState& state, const Consensus::Params& consensusParams, const CBlockIndex* pindexPrev, int64_t nAdjustedTime)
 {
-    const int nHeight = pindexPrev == NULL ? 0 : pindexPrev->nHeight + 1;
+    assert(pindexPrev != NULL);
+    const int nHeight = pindexPrev->nHeight + 1;
     // Check proof of work
     if (block.nBits != GetNextWorkRequired(pindexPrev, &block, consensusParams))
         return state.DoS(100, false, REJECT_INVALID, "bad-diffbits", false, "incorrect proof of work");