diff --git a/openmp/runtime/src/kmp.h b/openmp/runtime/src/kmp.h
index d5d667c32c643..a2cacc8792b15 100644
--- a/openmp/runtime/src/kmp.h
+++ b/openmp/runtime/src/kmp.h
@@ -821,7 +821,7 @@ class KMPAffinity {
 typedef KMPAffinity::Mask kmp_affin_mask_t;
 extern KMPAffinity *__kmp_affinity_dispatch;
 
-#ifndef KMP_OS_AIX
+#if !KMP_OS_AIX
 class kmp_affinity_raii_t {
   kmp_affin_mask_t *mask;
   bool restored;
diff --git a/openmp/runtime/src/kmp_affinity.cpp b/openmp/runtime/src/kmp_affinity.cpp
index f2520db145552..a6065fe792d55 100644
--- a/openmp/runtime/src/kmp_affinity.cpp
+++ b/openmp/runtime/src/kmp_affinity.cpp
@@ -5468,7 +5468,7 @@ void __kmp_affinity_bind_init_mask(int gtid) {
     __kmp_set_system_affinity(th->th.th_affin_mask, FALSE);
   } else
 #endif
-#ifndef KMP_OS_AIX
+#if !KMP_OS_AIX
     // Do not set the full mask as the init mask on AIX.
     __kmp_set_system_affinity(th->th.th_affin_mask, TRUE);
 #endif
diff --git a/openmp/runtime/src/kmp_platform.h b/openmp/runtime/src/kmp_platform.h
index 80afba6c6af2e..609b7c4688842 100644
--- a/openmp/runtime/src/kmp_platform.h
+++ b/openmp/runtime/src/kmp_platform.h
@@ -27,6 +27,7 @@
 #define KMP_OS_SOLARIS 0
 #define KMP_OS_WASI 0
 #define KMP_OS_EMSCRIPTEN 0
+#define KMP_OS_AIX 0
 #define KMP_OS_UNIX 0 /* disjunction of KMP_OS_LINUX, KMP_OS_DARWIN etc. */
 
 #ifdef _WIN32
@@ -163,11 +164,11 @@
 #undef KMP_ARCH_PPC64_ELFv1
 #define KMP_ARCH_PPC64_ELFv1 1
 #endif
-#elif defined KMP_OS_AIX
+#elif KMP_OS_AIX
 #undef KMP_ARCH_PPC64_XCOFF
 #define KMP_ARCH_PPC64_XCOFF 1
 #endif
-#elif defined(__powerpc__) && defined(KMP_OS_AIX)
+#elif defined(__powerpc__) && KMP_OS_AIX
 #undef KMP_ARCH_PPC_XCOFF
 #define KMP_ARCH_PPC_XCOFF 1
 #undef KMP_ARCH_PPC
diff --git a/openmp/runtime/src/kmp_wrapper_getpid.h b/openmp/runtime/src/kmp_wrapper_getpid.h
index 6b41dfcc20880..c6c7ac01799a0 100644
--- a/openmp/runtime/src/kmp_wrapper_getpid.h
+++ b/openmp/runtime/src/kmp_wrapper_getpid.h
@@ -17,7 +17,7 @@
 
 // On Unix-like systems (Linux* OS and OS X*) getpid() is declared in standard
 // headers.
-#if !defined(KMP_OS_AIX) && !defined(KMP_OS_HAIKU)
+#if !KMP_OS_AIX && !KMP_OS_HAIKU
 #include <sys/syscall.h>
 #endif
 #include <sys/types.h>