diff --git a/common/types_template.go b/common/types_template.go
new file mode 100644
index 0000000000..1c82a36dc5
--- /dev/null
+++ b/common/types_template.go
@@ -0,0 +1,48 @@
+// +build none
+//sed -e 's/_N_/Hash/g' -e 's/_S_/32/g' -e '1d' types_template.go | gofmt -w hash.go
+
+package common
+
+import "math/big"
+
+type _N_ [_S_]byte
+
+func BytesTo_N_(b []byte) _N_ {
+	var h _N_
+	h.SetBytes(b)
+	return h
+}
+func StringTo_N_(s string) _N_ { return BytesTo_N_([]byte(s)) }
+func BigTo_N_(b *big.Int) _N_  { return BytesTo_N_(b.Bytes()) }
+func HexTo_N_(s string) _N_    { return BytesTo_N_(FromHex(s)) }
+
+// Don't use the default 'String' method in case we want to overwrite
+
+// Get the string representation of the underlying hash
+func (h _N_) Str() string   { return string(h[:]) }
+func (h _N_) Bytes() []byte { return h[:] }
+func (h _N_) Big() *big.Int { return Bytes2Big(h[:]) }
+func (h _N_) Hex() string   { return "0x" + Bytes2Hex(h[:]) }
+
+// Sets the hash to the value of b. If b is larger than len(h) it will panic
+func (h *_N_) SetBytes(b []byte) {
+	// Use the right most bytes
+	if len(b) > len(h) {
+		b = b[len(b)-_S_:]
+	}
+
+	// Reverse the loop
+	for i := len(b) - 1; i >= 0; i-- {
+		h[_S_-len(b)+i] = b[i]
+	}
+}
+
+// Set string `s` to h. If s is larger than len(h) it will panic
+func (h *_N_) SetString(s string) { h.SetBytes([]byte(s)) }
+
+// Sets h to other
+func (h *_N_) Set(other _N_) {
+	for i, v := range other {
+		h[i] = v
+	}
+}
diff --git a/core/chain_manager.go b/core/chain_manager.go
index 5316a34230..0251f7c724 100644
--- a/core/chain_manager.go
+++ b/core/chain_manager.go
@@ -37,8 +37,8 @@ func CalcDifficulty(block, parent *types.Header) *big.Int {
 		diff.Sub(parent.Difficulty, adjust)
 	}
 
-	if diff.Cmp(GenesisDiff) < 0 {
-		return GenesisDiff
+	if diff.Cmp(min) < 0 {
+		return min
 	}
 
 	return diff