diff --git a/src/pow.cpp b/src/pow.cpp
--- a/src/pow.cpp
+++ b/src/pow.cpp
@@ -96,10 +96,8 @@
                              const CBlockHeader *pblock, const Config &config) {
     const Consensus::Params &params = config.GetChainParams().GetConsensus();
 
-    // Genesis block
-    if (pindexPrev == nullptr) {
-        return UintToArith256(params.powLimit).GetCompact();
-    }
+    // GetNextWorkRequired should never be called on the genesis block
+    assert(pindexPrev != nullptr);
 
     // Special rule for regtest: we never retarget.
     if (params.fPowNoRetargeting) {
diff --git a/src/validation.cpp b/src/validation.cpp
--- a/src/validation.cpp
+++ b/src/validation.cpp
@@ -1642,7 +1642,11 @@
                          CValidationState &state, CBlockIndex *pindex,
                          CCoinsViewCache &view, bool fJustCheck = false) {
     AssertLockHeld(cs_main);
-
+    assert(pindex);
+    // pindex->phashBlock can be null if called by
+    // CreateNewBlock/TestBlockValidity
+    assert((pindex->phashBlock == nullptr) ||
+           (*pindex->phashBlock == block.GetHash()));
     int64_t nTimeStart = GetTimeMicros();
 
     // Check it again in case a previous version let a bad block in
@@ -3566,7 +3570,8 @@
     const Consensus::Params &consensusParams =
         config.GetChainParams().GetConsensus();
 
-    const int nHeight = pindexPrev == nullptr ? 0 : pindexPrev->nHeight + 1;
+    assert(pindexPrev != nullptr);
+    const int nHeight = pindexPrev->nHeight + 1;
 
     // Check proof of work
     if (block.nBits != GetNextWorkRequired(pindexPrev, &block, config)) {