diff --git a/clang/include/clang/AST/UnresolvedSet.h b/clang/include/clang/AST/UnresolvedSet.h
--- a/clang/include/clang/AST/UnresolvedSet.h
+++ b/clang/include/clang/AST/UnresolvedSet.h
@@ -114,9 +114,17 @@
     I.I->set(New, AS);
   }
 
-  void erase(unsigned I) { decls()[I] = decls().pop_back_val(); }
+  void erase(unsigned I) {
+    auto val = decls().pop_back_val();
+    if (I < size())
+      decls()[I] = val;
+  }
 
-  void erase(iterator I) { *I.I = decls().pop_back_val(); }
+  void erase(iterator I) {
+    auto val = decls().pop_back_val();
+    if (I != end())
+      *I.I = val;
+  }
 
   void setAccess(iterator I, AccessSpecifier AS) { I.I->setAccess(AS); }
 
diff --git a/clang/unittests/AST/CMakeLists.txt b/clang/unittests/AST/CMakeLists.txt
--- a/clang/unittests/AST/CMakeLists.txt
+++ b/clang/unittests/AST/CMakeLists.txt
@@ -35,6 +35,7 @@
   StructuralEquivalenceTest.cpp
   TemplateNameTest.cpp
   TypePrinterTest.cpp
+  UnresolvedSetTest.cpp
   )
 
 clang_target_link_libraries(ASTTests
diff --git a/clang/unittests/AST/UnresolvedSetTest.cpp b/clang/unittests/AST/UnresolvedSetTest.cpp
new file mode 100644
--- /dev/null
+++ b/clang/unittests/AST/UnresolvedSetTest.cpp
@@ -0,0 +1,115 @@
+#include "clang/AST/UnresolvedSet.h"
+#include "gtest/gtest.h"
+
+namespace clang {
+class NamedDecl {
+  int dummy;
+
+public:
+  NamedDecl() {}
+};
+} // namespace clang
+
+using namespace clang;
+
+class UnresolvedSetTest : public ::testing::Test {
+protected:
+  NamedDecl n0, n1, n2, n3;
+  UnresolvedSet<2> set;
+
+  void SetUp() override {
+    set.addDecl(&n0);
+    set.addDecl(&n1);
+    set.addDecl(&n2);
+    set.addDecl(&n3);
+  }
+};
+
+TEST_F(UnresolvedSetTest, Size) { EXPECT_EQ(set.size(), 4u); }
+
+TEST_F(UnresolvedSetTest, ArrayOperator) {
+  EXPECT_EQ(set[0].getDecl(), &n0);
+  EXPECT_EQ(set[1].getDecl(), &n1);
+  EXPECT_EQ(set[2].getDecl(), &n2);
+  EXPECT_EQ(set[3].getDecl(), &n3);
+}
+
+TEST_F(UnresolvedSetTest, EraseIntegerFromStart) {
+  set.erase(0);
+  EXPECT_EQ(set.size(), 3u);
+  EXPECT_EQ(set[0].getDecl(), &n3);
+  EXPECT_EQ(set[1].getDecl(), &n1);
+  EXPECT_EQ(set[2].getDecl(), &n2);
+
+  set.erase(0);
+  EXPECT_EQ(set.size(), 2u);
+  EXPECT_EQ(set[0].getDecl(), &n2);
+  EXPECT_EQ(set[1].getDecl(), &n1);
+
+  set.erase(0);
+  EXPECT_EQ(set.size(), 1u);
+  EXPECT_EQ(set[0].getDecl(), &n1);
+
+  set.erase(0);
+  EXPECT_EQ(set.size(), 0u);
+}
+
+TEST_F(UnresolvedSetTest, EraseIntegerFromEnd) {
+  set.erase(3);
+  EXPECT_EQ(set.size(), 3u);
+  EXPECT_EQ(set[0].getDecl(), &n0);
+  EXPECT_EQ(set[1].getDecl(), &n1);
+  EXPECT_EQ(set[2].getDecl(), &n2);
+
+  set.erase(2);
+  EXPECT_EQ(set.size(), 2u);
+  EXPECT_EQ(set[0].getDecl(), &n0);
+  EXPECT_EQ(set[1].getDecl(), &n1);
+
+  set.erase(1);
+  EXPECT_EQ(set.size(), 1u);
+  EXPECT_EQ(set[0].getDecl(), &n0);
+
+  set.erase(0);
+  EXPECT_EQ(set.size(), 0u);
+}
+
+TEST_F(UnresolvedSetTest, EraseIteratorFromStart) {
+  set.erase(set.begin());
+  EXPECT_EQ(set.size(), 3u);
+  EXPECT_EQ(set[0].getDecl(), &n3);
+  EXPECT_EQ(set[1].getDecl(), &n1);
+  EXPECT_EQ(set[2].getDecl(), &n2);
+
+  set.erase(set.begin());
+  EXPECT_EQ(set.size(), 2u);
+  EXPECT_EQ(set[0].getDecl(), &n2);
+  EXPECT_EQ(set[1].getDecl(), &n1);
+
+  set.erase(set.begin());
+  EXPECT_EQ(set.size(), 1u);
+  EXPECT_EQ(set[0].getDecl(), &n1);
+
+  set.erase(set.begin());
+  EXPECT_EQ(set.size(), 0u);
+}
+
+TEST_F(UnresolvedSetTest, EraseIteratorFromEnd) {
+  set.erase(--set.end());
+  EXPECT_EQ(set.size(), 3u);
+  EXPECT_EQ(set[0].getDecl(), &n0);
+  EXPECT_EQ(set[1].getDecl(), &n1);
+  EXPECT_EQ(set[2].getDecl(), &n2);
+
+  set.erase(--set.end());
+  EXPECT_EQ(set.size(), 2u);
+  EXPECT_EQ(set[0].getDecl(), &n0);
+  EXPECT_EQ(set[1].getDecl(), &n1);
+
+  set.erase(--set.end());
+  EXPECT_EQ(set.size(), 1u);
+  EXPECT_EQ(set[0].getDecl(), &n0);
+
+  set.erase(--set.end());
+  EXPECT_EQ(set.size(), 0u);
+}