diff --git a/flang/runtime/complex-reduction.h b/flang/runtime/complex-reduction.h
--- a/flang/runtime/complex-reduction.h
+++ b/flang/runtime/complex-reduction.h
@@ -20,7 +20,7 @@
 
 struct CppDescriptor; /* dummy type name for Fortran::runtime::Descriptor */
 
-#ifdef _MSC_VER
+#if defined(_MSC_VER) && !(defined(__clang_major__) && __clang_major__ >= 12)
 typedef _Fcomplex float_Complex_t;
 typedef _Dcomplex double_Complex_t;
 typedef _Lcomplex long_double_Complex_t;
diff --git a/flang/runtime/complex-reduction.c b/flang/runtime/complex-reduction.c
--- a/flang/runtime/complex-reduction.c
+++ b/flang/runtime/complex-reduction.c
@@ -23,7 +23,7 @@
 /* Not all environments define CMPLXF, CMPLX, CMPLXL. */
 
 #ifndef CMPLXF
-#if __clang_major__ >= 12
+#if defined(__clang_major__) && (__clang_major__ >= 12)
 #define CMPLXF __builtin_complex
 #else
 static float_Complex_t CMPLXF(float r, float i) {
@@ -39,7 +39,7 @@
 #endif
 
 #ifndef CMPLX
-#if __clang_major__ >= 12
+#if defined(__clang_major__) && (__clang_major__ >= 12)
 #define CMPLX __builtin_complex
 #else
 static double_Complex_t CMPLX(double r, double i) {
@@ -55,7 +55,7 @@
 #endif
 
 #ifndef CMPLXL
-#if __clang_major__ >= 12
+#if defined(__clang_major__) && (__clang_major__ >= 12)
 #define CMPLXL __builtin_complex
 #else
 static long_double_Complex_t CMPLXL(long double r, long double i) {