diff --git a/unittests/ADT/DeltaAlgorithmTest.cpp b/unittests/ADT/DeltaAlgorithmTest.cpp
index 362892207f5..a1884cd8f3a 100644
--- a/unittests/ADT/DeltaAlgorithmTest.cpp
+++ b/unittests/ADT/DeltaAlgorithmTest.cpp
@@ -13,6 +13,8 @@
 #include <cstdarg>
 using namespace llvm;
 
+namespace std {
+
 std::ostream &operator<<(std::ostream &OS,
                          const std::set<unsigned> &S) {
   OS << "{";
@@ -26,6 +28,8 @@ std::ostream &operator<<(std::ostream &OS,
   return OS;
 }
 
+}
+
 namespace {
 
 class FixedDeltaAlgorithm : public DeltaAlgorithm {