diff --git a/implementations/cpp/Makefile b/implementations/cpp/Makefile
index 173c8a8..651ec38 100644
--- a/implementations/cpp/Makefile
+++ b/implementations/cpp/Makefile
@@ -1,9 +1,11 @@
-CXX=g++ -std=c++14 -Wall -Wextra -Werror -O0 -I googletest
+CXX=g++ -std=c++14 -Wall -Wextra -Werror -g -O0 -I googletest
 
-test: m
+test: all
 	./m
 
-m: main.cpp preserves.hpp preserves_text.hpp googletest.a
+all: m
+
+m: main.cpp preserves.hpp preserves_text.hpp preserves_binary.hpp googletest.a
 	$(CXX) -o $@ main.cpp googletest.a
 
 googletest.a: googletest/src/gtest-all.o googletest/src/gtest_main.o
diff --git a/implementations/cpp/preserves.hpp b/implementations/cpp/preserves.hpp
index 84d8e08..aa019c8 100644
--- a/implementations/cpp/preserves.hpp
+++ b/implementations/cpp/preserves.hpp
@@ -63,6 +63,7 @@ namespace Preserves {
 
         static Value from_unsigned(uint64_t i) { return from_int(i); }
         static Value from_signed(int64_t i) { return from_int(i); }
+        static Value from_bignum(std::vector<uint8_t> const& v);
 
         static Value from_number(uint64_t i) { return from_int(i); }
         static Value from_number(int64_t i) { return from_int(i); }
@@ -120,6 +121,9 @@ namespace Preserves {
         boost::optional<int64_t> as_signed() const;
         int64_t to_signed() const { return as_signed().value(); }
 
+        boost::optional<std::vector<uint8_t> const&> as_bignum() const;
+        std::vector<uint8_t> const& to_bignum() const { return as_bignum().value(); }
+
         boost::optional<std::string const&> as_string() const;
         std::string const& to_string() const { return as_string().value(); }
 
@@ -166,6 +170,7 @@ namespace Preserves {
         virtual boost::optional<double> as_double() const { return boost::none; }
         virtual boost::optional<uint64_t> as_unsigned() const { return boost::none; }
         virtual boost::optional<int64_t> as_signed() const { return boost::none; }
+        virtual boost::optional<std::vector<uint8_t> const&> as_bignum() const { return boost::none; }
         virtual boost::optional<std::string const&> as_string() const { return boost::none; }
         virtual boost::optional<std::vector<uint8_t> const&> as_bytes() const { return boost::none; }
         virtual boost::optional<std::string const&> as_symbol() const { return boost::none; }
@@ -267,6 +272,7 @@ namespace Preserves {
                 return boost::none;
             }
         });
+    PRESERVES_ATOMIC_VALUE_CLASS(BigNum, std::vector<uint8_t>, std::vector<uint8_t> const&, ValueKind::SignedInteger, as_bignum,);
     PRESERVES_ATOMIC_VALUE_CLASS(String, std::string, std::string const&, ValueKind::String, as_string,);
     PRESERVES_ATOMIC_VALUE_CLASS(ByteString, std::vector<uint8_t>, std::vector<uint8_t> const&, ValueKind::ByteString, as_bytes,);
     PRESERVES_ATOMIC_VALUE_CLASS(Symbol, std::string, std::string const&, ValueKind::Symbol, as_symbol,);
@@ -458,6 +464,7 @@ namespace Preserves {
     PRESERVES_DELEGATE_CAST(double, as_double);
     PRESERVES_DELEGATE_CAST(uint64_t, as_unsigned);
     PRESERVES_DELEGATE_CAST(int64_t, as_signed);
+    PRESERVES_DELEGATE_CAST(std::vector<uint8_t> const&, as_bignum);
     PRESERVES_DELEGATE_CAST(std::string const&, as_string);
     PRESERVES_DELEGATE_CAST(std::vector<uint8_t> const&, as_bytes);
     PRESERVES_DELEGATE_CAST(std::string const&, as_symbol);
@@ -473,6 +480,21 @@ namespace Preserves {
     template <typename T> boost::optional<Value<T>> Value<T>::get(size_t index) const { return p->get(index); }
     template <typename T> size_t Value<T>::size() const { return p->size(); }
 
+    bool bignum_lt(std::vector<uint8_t> const& a, std::vector<uint8_t> const& b) {
+        bool aNegative = (a.size() > 0) && (a[0] & 0x80);
+        bool bNegative = (b.size() > 0) && (b[0] & 0x80);
+        if (aNegative != bNegative) return aNegative;
+        if (aNegative) {
+            if (a.size() > b.size()) return true;
+            if (a.size() < b.size()) return false;
+            return a < b;
+        } else {
+            if (a.size() > b.size()) return false;
+            if (a.size() < b.size()) return true;
+            return a < b;
+        }
+    }
+
     template <typename T>
     bool operator<(Value<T> const& a, Value<T> const &b) {
         auto aKind = a.value_kind();
@@ -494,7 +516,19 @@ namespace Preserves {
                     if (auto bv = b.as_signed()) {
                         return false;
                     } else {
-                        return a.to_unsigned() < b.to_unsigned();
+                        if (auto av = a.as_unsigned()) {
+                            if (auto bv = b.as_unsigned()) {
+                                return *av < *bv;
+                            } else {
+                                return true;
+                            }
+                        } else {
+                            if (auto bv = b.as_unsigned()) {
+                                return false;
+                            } else {
+                                return bignum_lt(a.to_bignum(), b.to_bignum());
+                            }
+                        }
                     }
                 }
             }
diff --git a/implementations/cpp/preserves_binary.hpp b/implementations/cpp/preserves_binary.hpp
index 50cbbc4..154dffe 100644
--- a/implementations/cpp/preserves_binary.hpp
+++ b/implementations/cpp/preserves_binary.hpp
@@ -45,9 +45,11 @@ namespace Preserves {
             // Can read max 9 bytes, each with 7 bits of payload, for 9*7 = 63 bits.
             for (size_t count = 0; count < 9; count++) {
                 int b = i.get();
-                if (b == i.eof()) return boost::none;
+                if (i.eof()) return boost::none;
                 n |= (b & 0x7f) << (count * 7);
-                if ((b & 0x80) == 0) return n;
+                if ((b & 0x80) == 0) {
+                    return n;
+                }
             }
             return boost::none;
         }
@@ -87,6 +89,13 @@ namespace Preserves {
             return v;
         }
 
+        boost::optional<Value<T>> next_bignum(size_t n) {
+            auto b = std::make_shared<BigNum<T>>(std::vector<uint8_t>());
+            b->_value().resize(n);
+            if (!next_chunk(&b->_value()[0], n)) return boost::none;
+            return Value<T>(b);
+        }
+
         boost::optional<Value<T>> next() {
             bool end_sentinel;
             return _next(end_sentinel);
@@ -95,7 +104,10 @@ namespace Preserves {
         boost::optional<Value<T>> _next(bool& end_sentinel) {
         more:
             end_sentinel = false;
-            switch (auto tag = BinaryTag(i.get())) {
+            auto tag = BinaryTag(i.get());
+            // std::cout << "tag " << std::hex << int(tag) << " pos " << i.tellg() - 1 << std::endl;
+            if (i.eof()) return boost::none;
+            switch (tag) {
                 case BinaryTag::False: return Value<T>::from_bool(false);
                 case BinaryTag::True: return Value<T>::from_bool(true);
                 case BinaryTag::Float: return next_float().map(Value<T>::from_float);
@@ -117,13 +129,14 @@ namespace Preserves {
                         return next_unsigned(n).map([](uint64_t v) { return Value<T>::from_int(int64_t(v)); });
                     }
                     if (n == 9) {
-                        // We can only handle this if it's unsigned and the first byte is 0.
-                        if (i.get() != 0) return boost::none;
-                        return next_unsigned(8).map(Value<T>::from_unsigned);
+                        // We can handle this with uint64_t if it's unsigned and the first byte is 0.
+                        if (i.get() == 0) return next_unsigned(8).map(Value<T>::from_unsigned);
                     }
-                    return boost::none;
+                    return next_bignum(n);
                 }
-                case BinaryTag::SignedInteger: return boost::none;
+                case BinaryTag::SignedInteger: return varint(i).flat_map([&](size_t len) {
+                    return next_bignum(len);
+                });
                 case BinaryTag::String: return varint(i).flat_map([&](size_t len)-> boost::optional<Value<T>> {
                     auto s = std::make_shared<String<T>>(std::string());
                     s->_value().resize(len);
@@ -161,7 +174,7 @@ namespace Preserves {
                         if (!v) return boost::none;
                         s->values.push_back(*v);
                     }
-                }                
+                }
                 case BinaryTag::Set: {
                     auto s = std::make_shared<Set<T>>();
                     while (true) {
@@ -189,4 +202,4 @@ namespace Preserves {
             }
         }
     };
-}
\ No newline at end of file
+}