diff --git a/llvm/include/llvm/ADT/edit_distance.h b/llvm/include/llvm/ADT/edit_distance.h
--- a/llvm/include/llvm/ADT/edit_distance.h
+++ b/llvm/include/llvm/ADT/edit_distance.h
@@ -57,6 +57,10 @@
   typename ArrayRef<T>::size_type m = FromArray.size();
   typename ArrayRef<T>::size_type n = ToArray.size();
 
+	// if either of the strings are empty, return the length of the other string.
+	if(m == 0) return n;
+	if(n == 0) return m;
+
   const unsigned SmallBufferSize = 64;
   unsigned SmallBuffer[SmallBufferSize];
   std::unique_ptr<unsigned[]> Allocated;
diff --git a/llvm/unittests/ADT/StringRefTest.cpp b/llvm/unittests/ADT/StringRefTest.cpp
--- a/llvm/unittests/ADT/StringRefTest.cpp
+++ b/llvm/unittests/ADT/StringRefTest.cpp
@@ -508,6 +508,11 @@
 }
 
 TEST(StringRefTest, EditDistance) {
+	StringRef StrNull;
+	StringRef StrEmpty("");
+
+	EXPECT_EQ(0U, StrNull.edit_distance(""));
+	EXPECT_EQ(0U, StrEmpty.edit_distance(""));
   StringRef Hello("hello");
   EXPECT_EQ(2U, Hello.edit_distance("hill"));