diff --git a/llvm/lib/Support/StringRef.cpp b/llvm/lib/Support/StringRef.cpp
index d7fa99dbde27..393504cf01b0 100644
--- a/llvm/lib/Support/StringRef.cpp
+++ b/llvm/lib/Support/StringRef.cpp
@@ -372,7 +372,7 @@ void StringRef::split(SmallVectorImpl<StringRef> &A, char Separator,
 size_t StringRef::count(StringRef Str) const {
   size_t Count = 0;
   size_t N = Str.size();
-  if (N > Length)
+  if (!N || N > Length)
     return 0;
   for (size_t i = 0, e = Length - N + 1; i < e;) {
     if (substr(i, N).equals(Str)) {
diff --git a/llvm/unittests/ADT/StringRefTest.cpp b/llvm/unittests/ADT/StringRefTest.cpp
index cbb2a30ff17a..9cb24bfdb4db 100644
--- a/llvm/unittests/ADT/StringRefTest.cpp
+++ b/llvm/unittests/ADT/StringRefTest.cpp
@@ -509,6 +509,7 @@ TEST(StringRefTest, Count) {
   EXPECT_EQ(1U, Str.count("hello"));
   EXPECT_EQ(1U, Str.count("ello"));
   EXPECT_EQ(0U, Str.count("zz"));
+  EXPECT_EQ(0U, Str.count(""));
 
   StringRef OverlappingAbba("abbabba");
   EXPECT_EQ(1U, OverlappingAbba.count("abba"));
diff --git a/polly/lib/Analysis/ScopDetection.cpp b/polly/lib/Analysis/ScopDetection.cpp
index cf6ba75648df..59176d2a0ae9 100644
--- a/polly/lib/Analysis/ScopDetection.cpp
+++ b/polly/lib/Analysis/ScopDetection.cpp
@@ -1653,7 +1653,8 @@ bool ScopDetection::isValidRegion(DetectionContext &Context) const {
                                             CurRegion.getExit(), DbgLoc);
   }
 
-  if (!CurRegion.getEntry()->getName().count(OnlyRegion)) {
+  if (!OnlyRegion.empty() &&
+      !CurRegion.getEntry()->getName().count(OnlyRegion)) {
     LLVM_DEBUG({
       dbgs() << "Region entry does not match -polly-region-only";
       dbgs() << "\n";