diff --git a/lib/mongo/util/bson_ruby.rb b/lib/mongo/util/bson_ruby.rb
index f15ab2a..ba50349 100644
--- a/lib/mongo/util/bson_ruby.rb
+++ b/lib/mongo/util/bson_ruby.rb
@@ -72,6 +72,11 @@ class BSON_RUBY
     buf.put_array(to_utf8(val.to_s).unpack("C*") << 0)
   end
 
+  def self.serialize_key(buf, key)
+    raise InvalidDocument, "Key names must not contain the NULL byte" if key.include? 0
+    self.serialize_cstr(buf, key)
+  end
+
   def to_a
     @buf.to_a
   end
@@ -365,7 +370,7 @@ class BSON_RUBY
 
   def serialize_null_element(buf, key)
     buf.put(NULL)
-    self.class.serialize_cstr(buf, key)
+    self.class.serialize_key(buf, key)
   end
 
   def serialize_dbref_element(buf, key, val)
@@ -377,7 +382,7 @@ class BSON_RUBY
 
   def serialize_binary_element(buf, key, val)
     buf.put(BINARY)
-    self.class.serialize_cstr(buf, key)
+    self.class.serialize_key(buf, key)
 
     bytes = val.to_a
     num_bytes = bytes.length
@@ -396,13 +401,13 @@ class BSON_RUBY
 
   def serialize_boolean_element(buf, key, val)
     buf.put(BOOLEAN)
-    self.class.serialize_cstr(buf, key)
+    self.class.serialize_key(buf, key)
     buf.put(val ? 1 : 0)
   end
 
   def serialize_date_element(buf, key, val)
     buf.put(DATE)
-    self.class.serialize_cstr(buf, key)
+    self.class.serialize_key(buf, key)
     millisecs = (val.to_f * 1000).to_i
     buf.put_long(millisecs)
   end
@@ -410,7 +415,7 @@ class BSON_RUBY
   def serialize_number_element(buf, key, val, type)
     if type == NUMBER
       buf.put(type)
-      self.class.serialize_cstr(buf, key)
+      self.class.serialize_key(buf, key)
       buf.put_double(val)
     else
       if val > 2**64 / 2 - 1 or val < -2**64 / 2
@@ -418,11 +423,11 @@ class BSON_RUBY
       end
       if val > 2**32 / 2 - 1 or val < -2**32 / 2
         buf.put(NUMBER_LONG)
-        self.class.serialize_cstr(buf, key)
+        self.class.serialize_key(buf, key)
         buf.put_long(val)
       else
         buf.put(type)
-        self.class.serialize_cstr(buf, key)
+        self.class.serialize_key(buf, key)
         buf.put_int(val)
       end
     end
@@ -430,7 +435,7 @@ class BSON_RUBY
 
   def serialize_object_element(buf, key, val, check_keys, opcode=OBJECT)
     buf.put(opcode)
-    self.class.serialize_cstr(buf, key)
+    self.class.serialize_key(buf, key)
     buf.put_array(BSON.new.serialize(val, check_keys).to_a)
   end
 
@@ -444,7 +449,7 @@ class BSON_RUBY
 
   def serialize_regex_element(buf, key, val)
     buf.put(REGEX)
-    self.class.serialize_cstr(buf, key)
+    self.class.serialize_key(buf, key)
 
     str = val.to_s.sub(/.*?:/, '')[0..-2] # Turn "(?xxx:yyy)" into "yyy"
     self.class.serialize_cstr(buf, str)
@@ -461,14 +466,14 @@ class BSON_RUBY
 
   def serialize_oid_element(buf, key, val)
     buf.put(OID)
-    self.class.serialize_cstr(buf, key)
+    self.class.serialize_key(buf, key)
 
     buf.put_array(val.to_a)
   end
 
   def serialize_string_element(buf, key, val, type)
     buf.put(type)
-    self.class.serialize_cstr(buf, key)
+    self.class.serialize_key(buf, key)
 
     # Make a hole for the length
     len_pos = buf.position
@@ -488,7 +493,7 @@ class BSON_RUBY
 
   def serialize_code_w_scope(buf, key, val)
     buf.put(CODE_W_SCOPE)
-    self.class.serialize_cstr(buf, key)
+    self.class.serialize_key(buf, key)
 
     # Make a hole for the length
     len_pos = buf.position
diff --git a/test/test_bson.rb b/test/test_bson.rb
index 6e52ce5..2a88230 100644
--- a/test/test_bson.rb
+++ b/test/test_bson.rb
@@ -321,4 +321,14 @@ class BSONTest < Test::Unit::TestCase
     assert_equal BSON.serialize(one).to_a, BSON.serialize(dup).to_a
   end
 
+  def test_null_character
+    doc = {"a" => "\x00"}
+
+    assert_equal doc, BSON.deserialize(BSON.serialize(doc).to_a)
+
+    assert_raise InvalidDocument do
+      BSON.serialize({"\x00" => "a"})
+    end
+  end
+
 end