diff --git a/clang/lib/Headers/__clang_cuda_cmath.h b/clang/lib/Headers/__clang_cuda_cmath.h
--- a/clang/lib/Headers/__clang_cuda_cmath.h
+++ b/clang/lib/Headers/__clang_cuda_cmath.h
@@ -12,7 +12,7 @@
 #error "This file is for CUDA compilation only."
 #endif
 
-#ifndef _OPENMP
+#ifndef __OPENMP_NVPTX__
 #include <limits>
 #endif
 
@@ -32,7 +32,7 @@
 // implementation.  Declaring in the global namespace and pulling into namespace
 // std covers all of the known knowns.
 
-#ifdef _OPENMP
+#ifdef __OPENMP_NVPTX__
 #define __DEVICE__ static constexpr __attribute__((always_inline, nothrow))
 #else
 #define __DEVICE__ static __device__ __inline__ __attribute__((always_inline))
@@ -69,7 +69,7 @@
 // Windows. For OpenMP we omit these as some old system headers have
 // non-conforming `isinf(float)` and `isnan(float)` implementations that return
 // an `int`. The system versions of these functions should be fine anyway.
-#if !defined(_MSC_VER) && !defined(_OPENMP)
+#if !defined(_MSC_VER) && !defined(__OPENMP_NVPTX__)
 __DEVICE__ bool isinf(float __x) { return ::__isinff(__x); }
 __DEVICE__ bool isinf(double __x) { return ::__isinf(__x); }
 __DEVICE__ bool isfinite(float __x) { return ::__finitef(__x); }
@@ -146,7 +146,7 @@
 // libdevice doesn't provide an implementation, and we don't want to be in the
 // business of implementing tricky libm functions in this header.
 
-#ifndef _OPENMP
+#ifndef __OPENMP_NVPTX__
 
 // Now we've defined everything we promised we'd define in
 // __clang_cuda_math_forward_declares.h.  We need to do two additional things to
@@ -463,7 +463,7 @@
 } // namespace std
 #endif
 
-#endif // _OPENMP
+#endif // __OPENMP_NVPTX__
 
 #undef __DEVICE__
 
diff --git a/clang/lib/Headers/__clang_cuda_device_functions.h b/clang/lib/Headers/__clang_cuda_device_functions.h
--- a/clang/lib/Headers/__clang_cuda_device_functions.h
+++ b/clang/lib/Headers/__clang_cuda_device_functions.h
@@ -10,7 +10,7 @@
 #ifndef __CLANG_CUDA_DEVICE_FUNCTIONS_H__
 #define __CLANG_CUDA_DEVICE_FUNCTIONS_H__
 
-#ifndef _OPENMP
+#ifndef __OPENMP_NVPTX__
 #if CUDA_VERSION < 9000
 #error This file is intended to be used with CUDA-9+ only.
 #endif
@@ -20,7 +20,7 @@
 // we implement in this file. We need static in order to avoid emitting unused
 // functions and __forceinline__ helps inlining these wrappers at -O1.
 #pragma push_macro("__DEVICE__")
-#ifdef _OPENMP
+#ifdef __OPENMP_NVPTX__
 #define __DEVICE__ static __attribute__((always_inline, nothrow))
 #else
 #define __DEVICE__ static __device__ __forceinline__
@@ -1466,14 +1466,14 @@
 
 // For OpenMP we require the user to include <time.h> as we need to know what
 // clock_t is on the system.
-#ifndef _OPENMP
+#ifndef __OPENMP_NVPTX__
 __DEVICE__ /* clock_t= */ int clock() { return __nvvm_read_ptx_sreg_clock(); }
 #endif
 __DEVICE__ long long clock64() { return __nvvm_read_ptx_sreg_clock64(); }
 
 // These functions shouldn't be declared when including this header
 // for math function resolution purposes.
-#ifndef _OPENMP
+#ifndef __OPENMP_NVPTX__
 __DEVICE__ void *memcpy(void *__a, const void *__b, size_t __c) {
   return __builtin_memcpy(__a, __b, __c);
 }
diff --git a/clang/lib/Headers/__clang_cuda_libdevice_declares.h b/clang/lib/Headers/__clang_cuda_libdevice_declares.h
--- a/clang/lib/Headers/__clang_cuda_libdevice_declares.h
+++ b/clang/lib/Headers/__clang_cuda_libdevice_declares.h
@@ -14,7 +14,7 @@
 extern "C" {
 #endif
 
-#if defined(_OPENMP)
+#if defined(__OPENMP_NVPTX__)
 #define __DEVICE__
 #elif defined(__CUDA__)
 #define __DEVICE__ __device__
diff --git a/clang/lib/Headers/__clang_cuda_math.h b/clang/lib/Headers/__clang_cuda_math.h
--- a/clang/lib/Headers/__clang_cuda_math.h
+++ b/clang/lib/Headers/__clang_cuda_math.h
@@ -12,7 +12,7 @@
 #error "This file is for CUDA compilation only."
 #endif
 
-#ifndef _OPENMP
+#ifndef __OPENMP_NVPTX__
 #if CUDA_VERSION < 9000
 #error This file is intended to be used with CUDA-9+ only.
 #endif
@@ -22,7 +22,7 @@
 // we implement in this file. We need static in order to avoid emitting unused
 // functions and __forceinline__ helps inlining these wrappers at -O1.
 #pragma push_macro("__DEVICE__")
-#ifdef _OPENMP
+#ifdef __OPENMP_NVPTX__
 #if defined(__cplusplus)
 #define __DEVICE__ static constexpr __attribute__((always_inline, nothrow))
 #else
@@ -36,7 +36,7 @@
 // because the OpenMP overlay requires constexpr functions here but prior to
 // c++14 void return functions could not be constexpr.
 #pragma push_macro("__DEVICE_VOID__")
-#ifdef _OPENMP && defined(__cplusplus) && __cplusplus < 201402L
+#ifdef __OPENMP_NVPTX__ && defined(__cplusplus) && __cplusplus < 201402L
 #define __DEVICE_VOID__ static __attribute__((always_inline, nothrow))
 #else
 #define __DEVICE_VOID__ __DEVICE__
diff --git a/clang/lib/Headers/openmp_wrappers/__clang_openmp_device_functions.h b/clang/lib/Headers/openmp_wrappers/__clang_openmp_device_functions.h
--- a/clang/lib/Headers/openmp_wrappers/__clang_openmp_device_functions.h
+++ b/clang/lib/Headers/openmp_wrappers/__clang_openmp_device_functions.h
@@ -22,11 +22,15 @@
 #endif
 
 #define __CUDA__
+#define __OPENMP_NVPTX__
+
 /// Include declarations for libdevice functions.
 #include <__clang_cuda_libdevice_declares.h>
 
 /// Provide definitions for these functions.
 #include <__clang_cuda_device_functions.h>
+
+#undef __OPENMP_NVPTX__
 #undef __CUDA__
 
 #ifdef __cplusplus
diff --git a/clang/lib/Headers/openmp_wrappers/cmath b/clang/lib/Headers/openmp_wrappers/cmath
--- a/clang/lib/Headers/openmp_wrappers/cmath
+++ b/clang/lib/Headers/openmp_wrappers/cmath
@@ -28,7 +28,9 @@
     device = {arch(nvptx, nvptx64)}, implementation = {extension(match_any)})
 
 #define __CUDA__
+#define __OPENMP_NVPTX__
 #include <__clang_cuda_cmath.h>
+#undef __OPENMP_NVPTX__
 #undef __CUDA__
 
 // Overloads not provided by the CUDA wrappers but by the CUDA system headers.
diff --git a/clang/lib/Headers/openmp_wrappers/math.h b/clang/lib/Headers/openmp_wrappers/math.h
--- a/clang/lib/Headers/openmp_wrappers/math.h
+++ b/clang/lib/Headers/openmp_wrappers/math.h
@@ -41,7 +41,9 @@
     device = {arch(nvptx, nvptx64)}, implementation = {extension(match_any)})
 
 #define __CUDA__
+#define __OPENMP_NVPTX__
 #include <__clang_cuda_math.h>
+#undef __OPENMP_NVPTX__
 #undef __CUDA__
 
 #pragma omp end declare variant