diff --git a/unittests/ADT/StringRefTest.cpp b/unittests/ADT/StringRefTest.cpp
index 315eacb..59eed54 100644
--- a/unittests/ADT/StringRefTest.cpp
+++ b/unittests/ADT/StringRefTest.cpp
@@ -456,4 +456,23 @@
   }
 }
 
+
+static const char* BadStrings[] = {
+    "18446744073709551617"  // value just over max
+  , "123456789012345678901" // value way too large
+  , "4t23v"                 // illegal decimal characters
+  , "0x123W56"              // illegal hex characters
+};
+
+
+TEST(StringRefTest, getAsUnsignedIntegerBadStrings) {
+  uint64_t U64;
+  for (size_t i = 0; i < array_lengthof(BadStrings); ++i) {
+    bool IsBadNumber = getAsUnsignedInteger(BadStrings[i], 0, U64);
+    ASSERT_TRUE(IsBadNumber);
+  }
+}
+
+
+
 } // end anonymous namespace