Index: source/Utility/ArchSpec.cpp
===================================================================
--- source/Utility/ArchSpec.cpp
+++ source/Utility/ArchSpec.cpp
@@ -904,8 +904,7 @@
       UpdateCore();
   }
   if (TripleEnvironmentIsUnspecifiedUnknown() &&
-      !other.TripleEnvironmentIsUnspecifiedUnknown() &&
-      !TripleVendorWasSpecified() && other.TripleVendorWasSpecified()) {
+      !other.TripleEnvironmentIsUnspecifiedUnknown()) {
     GetTriple().setEnvironment(other.GetTriple().getEnvironment());
   }
   // If this and other are both arm ArchSpecs and this ArchSpec is a generic
Index: unittests/Utility/ArchSpecTest.cpp
===================================================================
--- unittests/Utility/ArchSpecTest.cpp
+++ unittests/Utility/ArchSpecTest.cpp
@@ -134,22 +134,46 @@
 }
 
 TEST(ArchSpecTest, MergeFrom) {
-  ArchSpec A;
-  ArchSpec B("x86_64-pc-linux");
-
-  EXPECT_FALSE(A.IsValid());
-  ASSERT_TRUE(B.IsValid());
-  EXPECT_EQ(llvm::Triple::ArchType::x86_64, B.GetTriple().getArch());
-  EXPECT_EQ(llvm::Triple::VendorType::PC, B.GetTriple().getVendor());
-  EXPECT_EQ(llvm::Triple::OSType::Linux, B.GetTriple().getOS());
-  EXPECT_EQ(ArchSpec::eCore_x86_64_x86_64, B.GetCore());
-
-  A.MergeFrom(B);
-  ASSERT_TRUE(A.IsValid());
-  EXPECT_EQ(llvm::Triple::ArchType::x86_64, A.GetTriple().getArch());
-  EXPECT_EQ(llvm::Triple::VendorType::PC, A.GetTriple().getVendor());
-  EXPECT_EQ(llvm::Triple::OSType::Linux, A.GetTriple().getOS());
-  EXPECT_EQ(ArchSpec::eCore_x86_64_x86_64, A.GetCore());
+  {
+    ArchSpec A;
+    ArchSpec B("x86_64-pc-linux");
+
+    EXPECT_FALSE(A.IsValid());
+    ASSERT_TRUE(B.IsValid());
+    EXPECT_EQ(llvm::Triple::ArchType::x86_64, B.GetTriple().getArch());
+    EXPECT_EQ(llvm::Triple::VendorType::PC, B.GetTriple().getVendor());
+    EXPECT_EQ(llvm::Triple::OSType::Linux, B.GetTriple().getOS());
+    EXPECT_EQ(ArchSpec::eCore_x86_64_x86_64, B.GetCore());
+
+    A.MergeFrom(B);
+    ASSERT_TRUE(A.IsValid());
+    EXPECT_EQ(llvm::Triple::ArchType::x86_64, A.GetTriple().getArch());
+    EXPECT_EQ(llvm::Triple::VendorType::PC, A.GetTriple().getVendor());
+    EXPECT_EQ(llvm::Triple::OSType::Linux, A.GetTriple().getOS());
+    EXPECT_EQ(ArchSpec::eCore_x86_64_x86_64, A.GetCore());
+  }
+  {
+    ArchSpec A("aarch64-unknown-unknown-unknown");
+    ArchSpec B("aarch64-unknown-linux-android");
+
+    EXPECT_TRUE(A.IsValid());
+    EXPECT_TRUE(B.IsValid());
+
+    EXPECT_EQ(llvm::Triple::ArchType::aarch64, B.GetTriple().getArch());
+    EXPECT_EQ(llvm::Triple::VendorType::UnknownVendor,
+              B.GetTriple().getVendor());
+    EXPECT_EQ(llvm::Triple::OSType::Linux, B.GetTriple().getOS());
+    EXPECT_EQ(llvm::Triple::EnvironmentType::Android,
+              B.GetTriple().getEnvironment());
+
+    A.MergeFrom(B);
+    EXPECT_EQ(llvm::Triple::ArchType::aarch64, A.GetTriple().getArch());
+    EXPECT_EQ(llvm::Triple::VendorType::UnknownVendor,
+              A.GetTriple().getVendor());
+    EXPECT_EQ(llvm::Triple::OSType::Linux, A.GetTriple().getOS());
+    EXPECT_EQ(llvm::Triple::EnvironmentType::Android,
+              A.GetTriple().getEnvironment());
+  }
 }
 
 TEST(ArchSpecTest, MergeFromMachOUnknown) {