diff --git a/libdevcore/FixedHash.h b/libdevcore/FixedHash.h
index c7c551c2b..d235dae41 100644
--- a/libdevcore/FixedHash.h
+++ b/libdevcore/FixedHash.h
@@ -31,6 +31,10 @@
 namespace dev
 {
 
+/// Compile-time calculation of Log2 of constant values.
+template <unsigned N> struct StaticLog2 { enum { result = 1 + StaticLog2<N/2>::result }; };
+template <> struct StaticLog2<1> { enum { result = 0 }; };
+
 extern std::random_device s_fixedHashEngine;
 
 /// Fixed-size raw-byte array container type, with an API optimised for storing hashes.
@@ -171,18 +175,21 @@ public:
 
 	template <unsigned P, unsigned M> inline FixedHash<M> bloomPart() const
 	{
-		static_assert((M & (M - 1)) == 0, "M must be power-of-two"); 
-		static const unsigned c_bloomBits = M * 8;
-		unsigned mask = c_bloomBits - 1;
-		unsigned bloomBytes = (dev::toLog2(c_bloomBits) + 7) / 8;
+		unsigned const c_bloomBits = M * 8;
+		unsigned const c_mask = c_bloomBits - 1;
+		unsigned const c_bloomBytes = (StaticLog2<c_bloomBits>::result + 7) / 8;
+
+		static_assert((M & (M - 1)) == 0, "M must be power-of-two");
+		static_assert(P * c_bloomBytes <= N, "out of range");
+
 		FixedHash<M> ret;
 		byte const* p = data();
 		for (unsigned i = 0; i < P; ++i)
 		{
 			unsigned index = 0;
-			for (unsigned j = 0; j < bloomBytes; ++j, ++p)
+			for (unsigned j = 0; j < c_bloomBytes; ++j, ++p)
 				index = (index << 8) | *p;
-			index &= mask;
+			index &= c_mask;
 			ret[M - 1 - index / 8] |= (1 << (index % 8));
 		}
 		return ret;