diff --git a/Godeps/Godeps.json b/Godeps/Godeps.json
index 0607990a8..6d68c18ec 100644
--- a/Godeps/Godeps.json
+++ b/Godeps/Godeps.json
@@ -21,8 +21,8 @@
 		},
 		{
 			"ImportPath": "github.com/ethereum/ethash",
-			"Comment": "v23.1-222-g173b8ff",
-			"Rev": "173b8ff953610c13710061e83b95b50c73d7ea50"
+			"Comment": "v23.1-227-g8f6ccaa",
+			"Rev": "8f6ccaaef9b418553807a73a95cb5f49cd3ea39f"
 		},
 		{
 			"ImportPath": "github.com/howeyc/fsnotify",
diff --git a/Godeps/_workspace/src/github.com/ethereum/ethash/ethash.go b/Godeps/_workspace/src/github.com/ethereum/ethash/ethash.go
index 73c5bf664..d0864da7f 100644
--- a/Godeps/_workspace/src/github.com/ethereum/ethash/ethash.go
+++ b/Godeps/_workspace/src/github.com/ethereum/ethash/ethash.go
@@ -100,19 +100,29 @@ type Light struct {
 func (l *Light) Verify(block pow.Block) bool {
 	// TODO: do ethash_quick_verify before getCache in order
 	// to prevent DOS attacks.
-	var (
-		blockNum   = block.NumberU64()
-		difficulty = block.Difficulty()
-		cache      = l.getCache(blockNum)
-		dagSize    = C.ethash_get_datasize(C.uint64_t(blockNum))
-	)
-	if l.test {
-		dagSize = dagSizeForTesting
-	}
+	blockNum := block.NumberU64()
 	if blockNum >= epochLength*2048 {
 		glog.V(logger.Debug).Infof("block number %d too high, limit is %d", epochLength*2048)
 		return false
 	}
+
+	difficulty := block.Difficulty()
+	/* Cannot happen if block header diff is validated prior to PoW, but can
+		 happen if PoW is checked first due to parallel PoW checking.
+		 We could check the minimum valid difficulty but for SoC we avoid (duplicating)
+	   Ethereum protocol consensus rules here which are not in scope of Ethash
+	*/
+	if difficulty.Cmp(common.Big0) == 0 {
+		glog.V(logger.Debug).Infof("invalid block difficulty")
+		return false
+	}
+
+	cache := l.getCache(blockNum)
+	dagSize := C.ethash_get_datasize(C.uint64_t(blockNum))
+
+	if l.test {
+		dagSize = dagSizeForTesting
+	}
 	// Recompute the hash using the cache.
 	hash := hashToH256(block.HashNoNonce())
 	ret := C.ethash_light_compute_internal(cache.ptr, dagSize, hash, C.uint64_t(block.Nonce()))
diff --git a/Godeps/_workspace/src/github.com/ethereum/ethash/ethash_test.go b/Godeps/_workspace/src/github.com/ethereum/ethash/ethash_test.go
index e6833e343..1e1de989d 100644
--- a/Godeps/_workspace/src/github.com/ethereum/ethash/ethash_test.go
+++ b/Godeps/_workspace/src/github.com/ethereum/ethash/ethash_test.go
@@ -11,6 +11,7 @@ import (
 	"testing"
 
 	"github.com/ethereum/go-ethereum/common"
+	"github.com/ethereum/go-ethereum/crypto"
 )
 
 func init() {
@@ -59,6 +60,14 @@ var validBlocks = []*testBlock{
 	},
 }
 
+var invalidZeroDiffBlock = testBlock{
+	number:      61440000,
+	hashNoNonce: crypto.Sha3Hash([]byte("foo")),
+	difficulty:  big.NewInt(0),
+	nonce:       0xcafebabec00000fe,
+	mixDigest:   crypto.Sha3Hash([]byte("bar")),
+}
+
 func TestEthashVerifyValid(t *testing.T) {
 	eth := New()
 	for i, block := range validBlocks {
@@ -68,6 +77,13 @@ func TestEthashVerifyValid(t *testing.T) {
 	}
 }
 
+func TestEthashVerifyInvalid(t *testing.T) {
+	eth := New()
+	if eth.Verify(&invalidZeroDiffBlock) {
+		t.Errorf("should not validate - we just ensure it does not panic on this block")
+	}
+}
+
 func TestEthashConcurrentVerify(t *testing.T) {
 	eth, err := NewForTesting()
 	if err != nil {
diff --git a/Godeps/_workspace/src/github.com/ethereum/ethash/src/libethash/internal.c b/Godeps/_workspace/src/github.com/ethereum/ethash/src/libethash/internal.c
index b28a59e43..338aa5ecd 100644
--- a/Godeps/_workspace/src/github.com/ethereum/ethash/src/libethash/internal.c
+++ b/Godeps/_workspace/src/github.com/ethereum/ethash/src/libethash/internal.c
@@ -284,13 +284,13 @@ bool ethash_quick_check_difficulty(
 	ethash_h256_t const* header_hash,
 	uint64_t const nonce,
 	ethash_h256_t const* mix_hash,
-	ethash_h256_t const* difficulty
+	ethash_h256_t const* boundary
 )
 {
 
 	ethash_h256_t return_hash;
 	ethash_quick_hash(&return_hash, header_hash, nonce, mix_hash);
-	return ethash_check_difficulty(&return_hash, difficulty);
+	return ethash_check_difficulty(&return_hash, boundary);
 }
 
 ethash_light_t ethash_light_new_internal(uint64_t cache_size, ethash_h256_t const* seed)
diff --git a/Godeps/_workspace/src/github.com/ethereum/ethash/src/libethash/internal.h b/Godeps/_workspace/src/github.com/ethereum/ethash/src/libethash/internal.h
index 4e2b695ac..26c395ad6 100644
--- a/Godeps/_workspace/src/github.com/ethereum/ethash/src/libethash/internal.h
+++ b/Godeps/_workspace/src/github.com/ethereum/ethash/src/libethash/internal.h
@@ -46,27 +46,36 @@ static inline void ethash_h256_reset(ethash_h256_t* hash)
 	memset(hash, 0, 32);
 }
 
-// Returns if hash is less than or equal to difficulty
+// Returns if hash is less than or equal to boundary (2^256/difficulty)
 static inline bool ethash_check_difficulty(
 	ethash_h256_t const* hash,
-	ethash_h256_t const* difficulty
+	ethash_h256_t const* boundary
 )
 {
-	// Difficulty is big endian
+	// Boundary is big endian
 	for (int i = 0; i < 32; i++) {
-		if (ethash_h256_get(hash, i) == ethash_h256_get(difficulty, i)) {
+		if (ethash_h256_get(hash, i) == ethash_h256_get(boundary, i)) {
 			continue;
 		}
-		return ethash_h256_get(hash, i) < ethash_h256_get(difficulty, i);
+		return ethash_h256_get(hash, i) < ethash_h256_get(boundary, i);
 	}
 	return true;
 }
 
+/**
+ *  Difficulty quick check for POW preverification
+ *
+ * @param header_hash      The hash of the header
+ * @param nonce            The block's nonce
+ * @param mix_hash         The mix digest hash
+ * @param boundary         The boundary is defined as (2^256 / difficulty)
+ * @return                 true for succesful pre-verification and false otherwise
+ */
 bool ethash_quick_check_difficulty(
 	ethash_h256_t const* header_hash,
 	uint64_t const nonce,
 	ethash_h256_t const* mix_hash,
-	ethash_h256_t const* difficulty
+	ethash_h256_t const* boundary
 );
 
 struct ethash_light {