diff --git a/src/pocketpy.cpp b/src/pocketpy.cpp
index 20addd09..73ddd61f 100644
--- a/src/pocketpy.cpp
+++ b/src/pocketpy.cpp
@@ -444,6 +444,14 @@ void init_builtins(VM* _vm) {
         return VAR(_CAST(i64, _0) % rhs);
     });
 
+    _vm->bind(_vm->_t(VM::tp_int), "bit_length(self)", [](VM* vm, ArgsView args) {
+        i64 x = CAST(i64, args[0]);
+        if(x < 0) x = -x;
+        int bits = 0;
+        while(x){ x >>= 1; bits++; }
+        return VAR(bits);
+    });
+
     _vm->bind__repr__(VM::tp_int, [](VM* vm, PyObject* obj) { return VAR(std::to_string(_CAST(i64, obj))); });
     _vm->bind__neg__(VM::tp_int, [](VM* vm, PyObject* obj) { return VAR(-_CAST(i64, obj)); });
     _vm->bind__hash__(VM::tp_int, [](VM* vm, PyObject* obj) { return _CAST(i64, obj); });
diff --git a/tests/01_int.py b/tests/01_int.py
index a1cb61a3..79089b2d 100644
--- a/tests/01_int.py
+++ b/tests/01_int.py
@@ -52,6 +52,11 @@ assert x == 3
 assert str(1) == '1'
 assert repr(1) == '1'
 
+# test bit_length
+assert (1).bit_length() == 1
+assert (2).bit_length() == 2
+assert (3).bit_length() == 2
+
 # test int()
 assert int() == 0
 assert int(True) == 1