diff --git a/ext/cbson/cbson.c b/ext/cbson/cbson.c
index f81bf58..4177f9d 100644
--- a/ext/cbson/cbson.c
+++ b/ext/cbson/cbson.c
@@ -353,7 +353,72 @@ static VALUE method_serialize(VALUE self, VALUE doc) {
     return result;
 }
 
+static VALUE get_value(const char* buffer, int* position, int type) {
+    VALUE value;
+    switch (type) {
+    case 1:
+        {
+            double d;
+            memcpy(&d, buffer + *position, 8);
+            value = DBL2NUM(d);
+            *position += 8;
+            break;
+        }
+    case 2:
+        {
+            *position += 4;
+            int value_length = strlen(buffer + *position);
+            value = rb_str_new(buffer+ *position, value_length);
+            *position += value_length + 1;
+            break;
+        }
+    case 8:
+        {
+            value = buffer[(*position)++] ? Qtrue : Qfalse;
+            break;
+        }
+    case 16:
+        {
+            int i;
+            memcpy(&i, buffer + *position, 4);
+            value = INT2FIX(i);
+            *position += 4;
+            break;
+        }
+    default:
+        rb_raise(rb_eTypeError, "no c decoder for this type yet (%d)", type);
+        break;
+    }
+    return value;
+}
+
+static VALUE elements_to_hash(const char* buffer, int max) {
+    VALUE hash = rb_hash_new();
+    int position = 0;
+    while (position < max) {
+        int type = (int)buffer[position++];
+        int name_length = strlen(buffer + position);
+        VALUE name = rb_str_new(buffer + position, name_length);
+        position += name_length + 1;
+        VALUE value = get_value(buffer, &position, type);
+        rb_hash_aset(hash, name, value);
+    }
+    return hash;
+}
+
+static VALUE method_deserialize(VALUE self, VALUE bson) {
+    const char* buffer = RSTRING(bson)->ptr;
+    int remaining = RSTRING(bson)->len;
+
+    // NOTE we just swallow the size and end byte here
+    buffer += 4;
+    remaining -= 5;
+
+    return elements_to_hash(buffer, remaining);
+}
+
 void Init_cbson() {
     VALUE CBson = rb_define_module("CBson");
     rb_define_module_function(CBson, "serialize", method_serialize, 1);
+    rb_define_module_function(CBson, "deserialize", method_deserialize, 1);
 }
diff --git a/lib/mongo/util/bson.rb b/lib/mongo/util/bson.rb
index 7f5d132..2f619ef 100644
--- a/lib/mongo/util/bson.rb
+++ b/lib/mongo/util/bson.rb
@@ -131,73 +131,86 @@ class BSON
       end
   end
 
-  def deserialize(buf=nil, parent=nil)
-    # If buf is nil, use @buf, assumed to contain already-serialized BSON.
-    # This is only true during testing.
-    if buf.is_a? String
-      @buf = ByteBuffer.new(buf) if buf
-    else
-      @buf = ByteBuffer.new(buf.to_a) if buf
-    end
-    @buf.rewind
-    @buf.get_int                # eat message size
-    doc = OrderedHash.new
-    while @buf.more?
-      type = @buf.get
-      case type
-      when STRING, CODE
-        key = deserialize_cstr(@buf)
-        doc[key] = deserialize_string_data(@buf)
-      when SYMBOL
-        key = deserialize_cstr(@buf)
-        doc[key] = deserialize_string_data(@buf).intern
-      when NUMBER
-        key = deserialize_cstr(@buf)
-        doc[key] = deserialize_number_data(@buf)
-      when NUMBER_INT
-        key = deserialize_cstr(@buf)
-        doc[key] = deserialize_number_int_data(@buf)
-      when OID
-        key = deserialize_cstr(@buf)
-        doc[key] = deserialize_oid_data(@buf)
-      when ARRAY
-        key = deserialize_cstr(@buf)
-        doc[key] = deserialize_array_data(@buf, doc)
-      when REGEX
-        key = deserialize_cstr(@buf)
-        doc[key] = deserialize_regex_data(@buf)
-      when OBJECT
-        key = deserialize_cstr(@buf)
-        doc[key] = deserialize_object_data(@buf, doc)
-      when BOOLEAN
-        key = deserialize_cstr(@buf)
-        doc[key] = deserialize_boolean_data(@buf)
-      when DATE
-        key = deserialize_cstr(@buf)
-        doc[key] = deserialize_date_data(@buf)
-      when NULL
-        key = deserialize_cstr(@buf)
-        doc[key] = nil
-      when UNDEFINED
-        key = deserialize_cstr(@buf)
-        doc[key] = Undefined.new
-      when REF
-        key = deserialize_cstr(@buf)
-        doc[key] = deserialize_dbref_data(@buf, key, parent)
-      when BINARY
-        key = deserialize_cstr(@buf)
-        doc[key] = deserialize_binary_data(@buf)
-      when CODE_W_SCOPE
-        # TODO CODE_W_SCOPE unimplemented; may be removed
-        raise "unimplemented type #{type}"
-      when EOO
-        break
+  begin
+    require 'mongo/ext/cbson'
+    def deserialize(buf=nil, parent=nil)
+      if buf.is_a? String
+        @buf = ByteBuffer.new(buf) if buf
       else
-        raise "Unknown type #{type}, key = #{key}"
+        @buf = ByteBuffer.new(buf.to_a) if buf
       end
+      @buf.rewind
+      CBson.deserialize(@buf.to_s)
+    end
+  rescue LoadError
+    def deserialize(buf=nil, parent=nil)
+      # If buf is nil, use @buf, assumed to contain already-serialized BSON.
+      # This is only true during testing.
+      if buf.is_a? String
+        @buf = ByteBuffer.new(buf) if buf
+      else
+        @buf = ByteBuffer.new(buf.to_a) if buf
+      end
+      @buf.rewind
+      @buf.get_int                # eat message size
+      doc = OrderedHash.new
+      while @buf.more?
+        type = @buf.get
+        case type
+        when STRING, CODE
+          key = deserialize_cstr(@buf)
+          doc[key] = deserialize_string_data(@buf)
+        when SYMBOL
+          key = deserialize_cstr(@buf)
+          doc[key] = deserialize_string_data(@buf).intern
+        when NUMBER
+          key = deserialize_cstr(@buf)
+          doc[key] = deserialize_number_data(@buf)
+        when NUMBER_INT
+          key = deserialize_cstr(@buf)
+          doc[key] = deserialize_number_int_data(@buf)
+        when OID
+          key = deserialize_cstr(@buf)
+          doc[key] = deserialize_oid_data(@buf)
+        when ARRAY
+          key = deserialize_cstr(@buf)
+          doc[key] = deserialize_array_data(@buf, doc)
+        when REGEX
+          key = deserialize_cstr(@buf)
+          doc[key] = deserialize_regex_data(@buf)
+        when OBJECT
+          key = deserialize_cstr(@buf)
+          doc[key] = deserialize_object_data(@buf, doc)
+        when BOOLEAN
+          key = deserialize_cstr(@buf)
+          doc[key] = deserialize_boolean_data(@buf)
+        when DATE
+          key = deserialize_cstr(@buf)
+          doc[key] = deserialize_date_data(@buf)
+        when NULL
+          key = deserialize_cstr(@buf)
+          doc[key] = nil
+        when UNDEFINED
+          key = deserialize_cstr(@buf)
+          doc[key] = Undefined.new
+        when REF
+          key = deserialize_cstr(@buf)
+          doc[key] = deserialize_dbref_data(@buf, key, parent)
+        when BINARY
+          key = deserialize_cstr(@buf)
+          doc[key] = deserialize_binary_data(@buf)
+        when CODE_W_SCOPE
+          # TODO CODE_W_SCOPE unimplemented; may be removed
+          raise "unimplemented type #{type}"
+        when EOO
+          break
+        else
+          raise "Unknown type #{type}, key = #{key}"
+        end
+      end
+      @buf.rewind
+      doc
     end
-    @buf.rewind
-    doc
   end
 
   # For debugging.