diff --git a/src/tests/util/serializer.cpp b/src/tests/util/serializer.cpp
index e3fe0c182..ffe169623 100644
--- a/src/tests/util/serializer.cpp
+++ b/src/tests/util/serializer.cpp
@@ -77,14 +77,24 @@ deserializer & operator>>(deserializer & d, list<int> & l) {
     return d;
 }
 
+void display(std::ostringstream const & out) {
+    std::cout << "OUT: ";
+    auto str = out.str();
+    for (auto c : str) {
+        std::cout << static_cast<int>(static_cast<unsigned char>(c)) << " ";
+    }
+    std::cout << "\n";
+}
+
 static void tst1() {
     std::ostringstream out;
     serializer s(out);
-    s.write_int(10); s.write_int(20); s.write_bool(false); s.write_string("hello"); s.write_int(30);
+    s.write_int(10); s.write_int(-20); s.write_bool(false); s.write_string("hello"); s.write_int(30);
+    display(out);
     std::istringstream in(out.str());
     deserializer d(in);
     lean_assert(d.read_int() == 10);
-    lean_assert(d.read_int() == 20);
+    lean_assert(d.read_int() == -20);
     lean_assert(!d.read_bool());
     lean_assert(d.read_string() == "hello");
     lean_assert(d.read_int() == 30);
@@ -99,13 +109,7 @@ static void tst2() {
     list<int> l3;
     l3 = cons(20, cons(30, l2));
     s << l1 << l2 << l3 << l2 << l3;
-
-    std::cout << "OUT: ";
-    auto str = out.str();
-    for (auto c : str) {
-        std::cout << static_cast<int>(c) << " ";
-    }
-    std::cout << "\n";
+    display(out);
 
     std::istringstream in(out.str());
     deserializer d(in);
@@ -131,6 +135,7 @@ static void tst3() {
     name n4(n1, "hello");
     name n5("simple");
     s << n1 << n2 << n3 << n4 << n2 << n5;
+    display(out);
     std::istringstream in(out.str());
     deserializer d(in);
     name m1, m2, m3, m4, m5, m6;
diff --git a/src/util/serializer.cpp b/src/util/serializer.cpp
index e22099ed3..657ff6e64 100644
--- a/src/util/serializer.cpp
+++ b/src/util/serializer.cpp
@@ -8,6 +8,19 @@ Author: Leonardo de Moura
 #include "util/serializer.h"
 
 namespace lean {
+void serializer_core::write_unsigned(unsigned i) {
+    static_assert(sizeof(i) == 4, "unexpected unsigned size");
+    m_out.put((i >> 24) & 0xff);
+    m_out.put((i >> 16) & 0xff);
+    m_out.put((i >> 8) & 0xff);
+    m_out.put(i & 0xff);
+}
+
+void serializer_core::write_int(int i) {
+    static_assert(sizeof(i) == 4, "unexpected int size");
+    write_unsigned(i);
+}
+
 std::string deserializer_core::read_string() {
     std::string r;
     while (true) {
@@ -18,4 +31,18 @@ std::string deserializer_core::read_string() {
     }
     return r;
 }
+
+unsigned deserializer_core::read_unsigned() {
+    unsigned r;
+    static_assert(sizeof(r) == 4, "unexpected unsigned size");
+    r  = static_cast<unsigned>(m_in.get()) << 24;
+    r |= static_cast<unsigned>(m_in.get()) << 16;
+    r |= static_cast<unsigned>(m_in.get()) << 8;
+    r |= static_cast<unsigned>(m_in.get());
+    return r;
+}
+
+int deserializer_core::read_int() {
+    return read_unsigned();
+}
 }
diff --git a/src/util/serializer.h b/src/util/serializer.h
index 4d0833278..25107cd63 100644
--- a/src/util/serializer.h
+++ b/src/util/serializer.h
@@ -22,8 +22,8 @@ public:
     serializer_core(std::ostream & out):m_out(out) {}
     void write_string(char const * str) { m_out.write(str, strlen(str) + 1); }
     void write_string(std::string const & str) { m_out.write(str.c_str(), str.size() + 1); }
-    void write_unsigned(unsigned i) { m_out.write(reinterpret_cast<char*>(&i), sizeof(i)); }
-    void write_int(int i) { m_out.write(reinterpret_cast<char*>(&i), sizeof(i)); }
+    void write_unsigned(unsigned i);
+    void write_int(int i);
     void write_char(char c) { m_out.put(c); }
     void write_bool(bool b) { m_out.put(b ? 1 : 0); }
 };
@@ -46,8 +46,8 @@ class deserializer_core {
 public:
     deserializer_core(std::istream & in):m_in(in) {}
     std::string read_string();
-    int read_int() { int r; m_in.read(reinterpret_cast<char*>(&r), sizeof(r)); return r; }
-    unsigned read_unsigned() { unsigned r; m_in.read(reinterpret_cast<char*>(&r), sizeof(r)); return r; }
+    unsigned read_unsigned();
+    int read_int();
     char read_char() { return m_in.get(); }
     bool read_bool() { return m_in.get() != 0; }
 };