diff --git a/tile/base/string_test.cc b/tile/base/string_test.cc
index ea204c8..b683493 100644
--- a/tile/base/string_test.cc
+++ b/tile/base/string_test.cc
@@ -191,6 +191,8 @@ TEST(String, TrimByCustset)
     ASSERT_EQ(" ", Trim("abcd abcd", "abcd"));
     ASSERT_EQ("abcd abc", Trim("abcd abcd", "d"));
     ASSERT_EQ("abcd abcd ", Trim("abcd abcd ", "d"));
+    ASSERT_EQ(" abcd abcd ", Trim(" abcd abcd ", "ad"));
+    ASSERT_EQ("bcd abc", Trim(" abcd abcd ", "ad "));
 }
 
 TEST(String, Split1)