diff --git a/dbus/dbus-string-util.c b/dbus/dbus-string-util.c
index aed9487..f2d1d69 100644
--- a/dbus/dbus-string-util.c
+++ b/dbus/dbus-string-util.c
@@ -512,7 +512,38 @@ _dbus_string_test (void)
   _dbus_assert (_dbus_string_get_length (&other) == i * 2 - 1);
   _dbus_assert (_dbus_string_equal_c_str (&other,
                                           "HelloHello WorldWorle"));
-  
+
+  if (!_dbus_string_replace_len (&str, 0, 5,
+                                 &other,
+                                 _dbus_string_get_length (&other) - 5,
+                                 5))
+    _dbus_assert_not_reached ("could not replace same length");
+
+  _dbus_assert (_dbus_string_get_length (&str) == i);
+  _dbus_assert (_dbus_string_get_length (&other) == i * 2 - 1);
+  _dbus_assert (_dbus_string_equal_c_str (&other,
+                                          "HelloHello WorldHello"));
+
+  if (!_dbus_string_replace_len (&str, 0, 5,
+                                 &other,
+                                 _dbus_string_get_length (&other) - 10,
+                                 10))
+    _dbus_assert_not_reached ("could not replace different length");
+
+  _dbus_assert (_dbus_string_get_length (&str) == i);
+  _dbus_assert (_dbus_string_get_length (&other) == 16);
+  _dbus_assert (_dbus_string_equal_c_str (&other,
+                                          "HelloHello Hello"));
+
+  if (!_dbus_string_replace_len (&str, 6, 5,
+                                 &other, 1, 2))
+    _dbus_assert_not_reached ("could not replace different length");
+
+  _dbus_assert (_dbus_string_get_length (&str) == i);
+  _dbus_assert (_dbus_string_get_length (&other) == 19);
+  _dbus_assert (_dbus_string_equal_c_str (&other,
+                                          "HWorldloHello Hello"));
+
   _dbus_string_free (&str);
   _dbus_string_free (&other);
   
diff --git a/dbus/dbus-string.c b/dbus/dbus-string.c
index 6b9b2bf..ce6919b 100644
--- a/dbus/dbus-string.c
+++ b/dbus/dbus-string.c
@@ -1668,11 +1668,33 @@ _dbus_string_replace_len (const DBusString *source,
   _dbus_assert (replace_at <= real_dest->len);
   _dbus_assert (replace_len <= real_dest->len - replace_at);
 
-  if (!copy (real_source, start, len,
-             real_dest, replace_at))
-    return FALSE;
+  if (len == replace_len)
+    memmove (real_dest->str + replace_at,
+             real_source->str + start, len);
+  else if (len < replace_len)
+    {
+      memmove (real_dest->str + replace_at,
+               real_source->str + start, len);
+      delete (real_dest, replace_at + len,
+              replace_len - len);
+    }
+  else /* if (len > replace_len) */
+    {
+      int diff;
+
+      diff = len - replace_len;
 
-  delete (real_dest, replace_at + len, replace_len);
+      /* First of all we check if destination string can be enlarged as
+       * required, then we overwrite previous bytes
+       */
+
+      if (!copy (real_source, start + replace_len, diff,
+                 real_dest, replace_at + replace_len))
+        return FALSE;
+
+      memmove (real_dest->str + replace_at,
+               real_source->str + start, replace_len);
+    }
 
   return TRUE;
 }