diff --git a/src/serialize.h b/src/serialize.h
index f87009855a..d2104672d8 100644
--- a/src/serialize.h
+++ b/src/serialize.h
@@ -206,6 +206,8 @@ template<typename Stream> inline void Unserialize(Stream& s, double& a  ) { a =
 template<typename Stream> inline void Serialize(Stream& s, bool a)    { char f=a; ser_writedata8(s, f); }
 template<typename Stream> inline void Unserialize(Stream& s, bool& a) { char f=ser_readdata8(s); a=f; }
 
+template <typename T> size_t GetSerializeSize(const T& t, int nType, int nVersion = 0);
+template <typename S, typename T> size_t GetSerializeSize(const S& s, const T& t);
 
 
 
@@ -359,6 +361,8 @@ I ReadVarInt(Stream& is)
 #define FLATDATA(obj) REF(CFlatData((char*)&(obj), (char*)&(obj) + sizeof(obj)))
 #define FIXEDBITSET(obj, size) REF(CFixedBitSet(REF(obj), (size)))
 #define DYNBITSET(obj) REF(CDynamicBitSet(REF(obj)))
+#define FIXEDVARINTSBITSET(obj, size) REF(CFixedVarIntsBitSet(REF(obj), (size)))
+#define AUTOBITSET(obj, size) REF(CAutoBitSet(REF(obj), (size)))
 #define VARINT(obj) REF(WrapVarInt(REF(obj)))
 #define COMPACTSIZE(obj) REF(CCompactSize(REF(obj)))
 #define LIMITED_STRING(obj,n) REF(LimitedString< n >(REF(obj)))
@@ -464,6 +468,101 @@ public:
     }
 };
 
+/**
+ * Stores a fixed size bitset as a series of VarInts. Each VarInt is an offset from the last entry and the sum of the
+ * last entry and the offset gives an index into the bitset for a set bit. The series of VarInts ends with a 0.
+ */
+class CFixedVarIntsBitSet
+{
+protected:
+    std::vector<bool>& vec;
+    size_t size;
+
+public:
+    CFixedVarIntsBitSet(std::vector<bool>& vecIn, size_t sizeIn) : vec(vecIn), size(sizeIn) {}
+
+    template<typename Stream>
+    void Serialize(Stream& s) const
+    {
+        int32_t last = -1;
+        for (int32_t i = 0; i < (int32_t)vec.size(); i++) {
+            if (vec[i]) {
+                WriteVarInt<Stream, uint32_t>(s, (uint32_t)(i - last));
+                last = i;
+            }
+        }
+        WriteVarInt(s, 0); // stopper
+    }
+
+    template<typename Stream>
+    void Unserialize(Stream& s)
+    {
+        vec.assign(size, false);
+
+        int32_t last = -1;
+        while(true) {
+            uint32_t offset = ReadVarInt<Stream, uint32_t>(s);
+            if (offset == 0) {
+                break;
+            }
+            int32_t idx = last + offset;
+            if (idx >= size) {
+                throw std::ios_base::failure("out of bounds index");
+            }
+            if (last != -1 && idx <= last) {
+                throw std::ios_base::failure("offset overflow");
+            }
+            vec[idx] = true;
+            last = idx;
+        }
+    }
+};
+
+/**
+ * Serializes either as a CFixedBitSet or CFixedVarIntsBitSet, depending on which would give a smaller size
+ */
+class CAutoBitSet
+{
+protected:
+    std::vector<bool>& vec;
+    size_t size;
+
+public:
+    explicit CAutoBitSet(std::vector<bool>& vecIn, size_t sizeIn) : vec(vecIn), size(sizeIn) {}
+
+    template<typename Stream>
+    void Serialize(Stream& s) const
+    {
+        assert(vec.size() == size);
+
+        size_t size1 = ::GetSerializeSize(s, CFixedBitSet(vec, size));
+        size_t size2 = ::GetSerializeSize(s, CFixedVarIntsBitSet(vec, size));
+
+        if (size1 < size2) {
+            ser_writedata8(s, 0);
+            s << FIXEDBITSET(vec, vec.size());
+        } else {
+            ser_writedata8(s, 1);
+            s << FIXEDVARINTSBITSET(vec, vec.size());
+        }
+    }
+
+    template<typename Stream>
+    void Unserialize(Stream& s)
+    {
+        uint8_t isVarInts = ser_readdata8(s);
+        if (isVarInts != 0 && isVarInts != 1) {
+            throw std::ios_base::failure("invalid value for isVarInts byte");
+        }
+
+        if (!isVarInts) {
+            s >> FIXEDBITSET(vec, size);
+        } else {
+            s >> FIXEDVARINTSBITSET(vec, size);
+        }
+    }
+};
+
 template<typename I>
 class CVarInt
 {
@@ -1093,7 +1192,7 @@ inline void WriteCompactSize(CSizeComputer &s, uint64_t nSize)
 }
 
 template <typename T>
-size_t GetSerializeSize(const T& t, int nType, int nVersion = 0)
+size_t GetSerializeSize(const T& t, int nType, int nVersion)
 {
     return (CSizeComputer(nType, nVersion) << t).size();
 }