diff --git a/clang/lib/Basic/Targets/Mips.cpp b/clang/lib/Basic/Targets/Mips.cpp
--- a/clang/lib/Basic/Targets/Mips.cpp
+++ b/clang/lib/Basic/Targets/Mips.cpp
@@ -195,11 +195,11 @@
   if (StringRef(CPU).startswith("octeon"))
     Builder.defineMacro("__OCTEON__");
 
-  // These shouldn't be defined for MIPS-I but there's no need to check
-  // for that since MIPS-I isn't supported.
-  Builder.defineMacro("__GCC_HAVE_SYNC_COMPARE_AND_SWAP_1");
-  Builder.defineMacro("__GCC_HAVE_SYNC_COMPARE_AND_SWAP_2");
-  Builder.defineMacro("__GCC_HAVE_SYNC_COMPARE_AND_SWAP_4");
+  if (CPU != "mips1") {
+    Builder.defineMacro("__GCC_HAVE_SYNC_COMPARE_AND_SWAP_1");
+    Builder.defineMacro("__GCC_HAVE_SYNC_COMPARE_AND_SWAP_2");
+    Builder.defineMacro("__GCC_HAVE_SYNC_COMPARE_AND_SWAP_4");
+  }
 
   // 32-bit MIPS processors don't have the necessary lld/scd instructions
   // found in 64-bit processors. In the case of O32 on a 64-bit processor,
diff --git a/clang/test/Preprocessor/predefined-macros.c b/clang/test/Preprocessor/predefined-macros.c
--- a/clang/test/Preprocessor/predefined-macros.c
+++ b/clang/test/Preprocessor/predefined-macros.c
@@ -118,12 +118,15 @@
 // RUN:   | FileCheck -match-full-lines %s --check-prefix=CHECK-SYNC_CAS_ARMv6
 // CHECK-SYNC_CAS_ARMv6-NOT: __GCC_HAVE_SYNC_COMPARE_AND_SWAP
 //
+// RUN: %clang_cc1 %s -E -dM -o - -triple mips -target-cpu mips1 \
+// RUN:   | FileCheck -match-full-lines %s --check-prefix=CHECK-SYNC_CAS_MIPS32_MIPS1
 // RUN: %clang_cc1 %s -E -dM -o - -triple mips -target-cpu mips2 \
 // RUN:   | FileCheck -match-full-lines %s --check-prefix=CHECK-SYNC_CAS_MIPS \
 // RUN:         --check-prefix=CHECK-SYNC_CAS_MIPS32
 // RUN: %clang_cc1 %s -E -dM -o - -triple mips64 -target-cpu mips3 \
 // RUN:   | FileCheck -match-full-lines %s --check-prefix=CHECK-SYNC_CAS_MIPS \
 // RUN:         --check-prefix=CHECK-SYNC_CAS_MIPS64
+// CHECK-SYNC_CAS_MIPS32_MIPS1-NOT: __GCC_HAVE_SYNC_COMPARE_AND_SWAP
 // CHECK-SYNC_CAS_MIPS: #define __GCC_HAVE_SYNC_COMPARE_AND_SWAP_1 1
 // CHECK-SYNC_CAS_MIPS: #define __GCC_HAVE_SYNC_COMPARE_AND_SWAP_2 1
 // CHECK-SYNC_CAS_MIPS: #define __GCC_HAVE_SYNC_COMPARE_AND_SWAP_4 1