diff --git a/libdevcore/FixedHash.h b/libdevcore/FixedHash.h
index 6aeb0a660..02d199f62 100644
--- a/libdevcore/FixedHash.h
+++ b/libdevcore/FixedHash.h
@@ -158,21 +158,25 @@ public:
 		return ret;
 	}
 
-	template <unsigned P, unsigned M> inline FixedHash& shiftBloom(FixedHash<M> const& _h) { return (*this |= _h.template nbloom<P, N>()); }
+	template <unsigned P, unsigned M> inline FixedHash& shiftBloom(FixedHash<M> const& _h)
+	{
+		return (*this |= _h.template nbloom<P, N>());
+	}
 
 	template <unsigned P, unsigned M> inline FixedHash<M> nbloom() const
 	{
-		static const unsigned c_bloomBytes = (M + 7) / 8;
-		unsigned mask = (1 << c_bloomBytes) - 1;
+		static const unsigned c_bloomBits = M * 8;
+		unsigned mask = c_bloomBits - 1;
+		unsigned bloomBytes = (dev::toLog2(c_bloomBits) + 7) / 8;
 		FixedHash<M> ret;
 		byte const* p = data();
 		for (unsigned i = 0; i < P; ++i)
 		{
 			unsigned index = 0;
-			for (unsigned j = 0; j < c_bloomBytes; ++j, ++p)
+			for (unsigned j = 0; j < bloomBytes; ++j, ++p)
 				index = (index << 8) | *p;
 			index &= mask;
-			ret[N - 1 - index / 8] |= (1 << (index % 8));
+			ret[M - 1 - index / 8] |= (1 << (index % 8));
 		}
 		return ret;
 	}