diff --git a/compiler-rt/lib/sanitizer_common/sanitizer_mac.h b/compiler-rt/lib/sanitizer_common/sanitizer_mac.h
--- a/compiler-rt/lib/sanitizer_common/sanitizer_mac.h
+++ b/compiler-rt/lib/sanitizer_common/sanitizer_mac.h
@@ -30,25 +30,24 @@
   bool current_instrumented;
 };
 
-enum MacosVersion {
-  MACOS_VERSION_UNINITIALIZED = 0,
-  MACOS_VERSION_UNKNOWN,
-  MACOS_VERSION_LEOPARD,
-  MACOS_VERSION_SNOW_LEOPARD,
-  MACOS_VERSION_LION,
-  MACOS_VERSION_MOUNTAIN_LION,
-  MACOS_VERSION_MAVERICKS,
-  MACOS_VERSION_YOSEMITE,
-  MACOS_VERSION_EL_CAPITAN,
-  MACOS_VERSION_SIERRA,
-  MACOS_VERSION_HIGH_SIERRA,
-  MACOS_VERSION_HIGH_SIERRA_DOT_RELEASE_4,
-  MACOS_VERSION_MOJAVE,
-  MACOS_VERSION_CATALINA,
-  MACOS_VERSION_UNKNOWN_NEWER
+struct MacosVersion {
+  u16 major;
+  u16 minor;
+
+  MacosVersion(u16 ten, u16 major, u16 minor = 0) : major(major), minor(minor) {
+    CHECK_EQ(ten, 10);
+  }
+
+  bool operator==(const MacosVersion &other) const {
+    return major == other.major && minor == other.minor;
+  }
+  bool operator>=(const MacosVersion &other) const {
+    return major >= other.major ||
+           (major == other.major && minor >= other.minor);
+  }
 };
 
-MacosVersion GetMacosVersion();
+MacosVersion GetMacosAlignedVersion();
 
 char **GetEnviron();
 
diff --git a/compiler-rt/lib/sanitizer_common/sanitizer_mac.cpp b/compiler-rt/lib/sanitizer_common/sanitizer_mac.cpp
--- a/compiler-rt/lib/sanitizer_common/sanitizer_mac.cpp
+++ b/compiler-rt/lib/sanitizer_common/sanitizer_mac.cpp
@@ -387,7 +387,7 @@
   // pthread_get_stacksize_np() returns an incorrect stack size for the main
   // thread on Mavericks. See
   // https://github.com/google/sanitizers/issues/261
-  if ((GetMacosVersion() >= MACOS_VERSION_MAVERICKS) && at_initialization &&
+  if ((GetMacosAlignedVersion() >= MacosVersion(10, 9)) && at_initialization &&
       stacksize == (1 << 19))  {
     struct rlimit rl;
     CHECK_EQ(getrlimit(RLIMIT_STACK, &rl), 0);
@@ -606,9 +606,7 @@
   return result;
 }
 
-MacosVersion cached_macos_version = MACOS_VERSION_UNINITIALIZED;
-
-MacosVersion GetMacosVersionInternal() {
+static MacosVersion GetMacosAlignedVersionInternal() {
   int mib[2] = { CTL_KERN, KERN_OSRELEASE };
   char version[100];
   uptr len = 0, maxlen = sizeof(version) / sizeof(version[0]);
@@ -618,47 +616,35 @@
   CHECK_LT(len, maxlen);
   CHECK_NE(internal_sysctl(mib, 2, version, &len, 0, 0), -1);
 
-  // Expect <major>.<minor>(.<patch>)
+  // Expect <major>.<minor>.<patch>
   CHECK_GE(len, 3);
   const char *p = version;
   int major = internal_simple_strtoll(p, &p, /*base=*/10);
-  if (*p != '.') return MACOS_VERSION_UNKNOWN;
+  CHECK_EQ(*p, '.');
   p += 1;
   int minor = internal_simple_strtoll(p, &p, /*base=*/10);
-  if (*p != '.') return MACOS_VERSION_UNKNOWN;
-
-  switch (major) {
-    case 9: return MACOS_VERSION_LEOPARD;
-    case 10: return MACOS_VERSION_SNOW_LEOPARD;
-    case 11: return MACOS_VERSION_LION;
-    case 12: return MACOS_VERSION_MOUNTAIN_LION;
-    case 13: return MACOS_VERSION_MAVERICKS;
-    case 14: return MACOS_VERSION_YOSEMITE;
-    case 15: return MACOS_VERSION_EL_CAPITAN;
-    case 16: return MACOS_VERSION_SIERRA;
-    case 17:
-      // Not a typo, 17.5 Darwin Kernel Version maps to High Sierra 10.13.4.
-      if (minor >= 5)
-        return MACOS_VERSION_HIGH_SIERRA_DOT_RELEASE_4;
-      return MACOS_VERSION_HIGH_SIERRA;
-    case 18: return MACOS_VERSION_MOJAVE;
-    case 19: return MACOS_VERSION_CATALINA;
-    default:
-      if (major < 9) return MACOS_VERSION_UNKNOWN;
-      return MACOS_VERSION_UNKNOWN_NEWER;
-  }
+  CHECK_EQ(*p, '.');
+
+  // Kernel version 17.5 maps to High Sierra 10.13.4.
+  if (major == 17 && minor == 5)
+    return MacosVersion(10, 13, 4);
+
+  int macos_major = major - 4;
+  return MacosVersion(10, macos_major, minor);
 }
 
-MacosVersion GetMacosVersion() {
-  atomic_uint32_t *cache =
-      reinterpret_cast<atomic_uint32_t*>(&cached_macos_version);
-  MacosVersion result =
-      static_cast<MacosVersion>(atomic_load(cache, memory_order_acquire));
-  if (result == MACOS_VERSION_UNINITIALIZED) {
-    result = GetMacosVersionInternal();
-    atomic_store(cache, result, memory_order_release);
+static_assert(sizeof(MacosVersion) == sizeof(uint32_t),
+              "MacosVersion cache size");
+static atomic_uint32_t cached_macos_version;
+
+MacosVersion GetMacosAlignedVersion() {
+  uint32_t result = atomic_load(&cached_macos_version, memory_order_acquire);
+  if (!result) {
+    MacosVersion version = GetMacosAlignedVersionInternal();
+    result = *reinterpret_cast<uint32_t *>(&version);
+    atomic_store(&cached_macos_version, result, memory_order_release);
   }
-  return result;
+  return *reinterpret_cast<MacosVersion *>(&result);
 }
 
 bool PlatformHasDifferentMemcpyAndMemmove() {
@@ -667,7 +653,7 @@
   // See also https://github.com/google/sanitizers/issues/34.
   // TODO(glider): need to check dynamically that memcpy() and memmove() are
   // actually the same function.
-  return GetMacosVersion() == MACOS_VERSION_SNOW_LEOPARD;
+  return GetMacosAlignedVersion() == MacosVersion(10, 6);
 }
 
 uptr GetRSS() {
@@ -716,7 +702,7 @@
 #if !SANITIZER_GO
   // Log with os_trace. This will make it into the crash log.
 #if SANITIZER_OS_TRACE
-  if (GetMacosVersion() >= MACOS_VERSION_YOSEMITE) {
+  if (GetMacosAlignedVersion() >= MacosVersion(10, 10)) {
     // os_trace requires the message (format parameter) to be a string literal.
     if (internal_strncmp(SanitizerToolName, "AddressSanitizer",
                          sizeof("AddressSanitizer") - 1) == 0)
@@ -805,7 +791,7 @@
   // Only use xnu_fast_mmap when on x86_64 and the OS supports it.
   use_xnu_fast_mmap =
 #if defined(__x86_64__)
-      GetMacosVersion() >= MACOS_VERSION_HIGH_SIERRA_DOT_RELEASE_4;
+      GetMacosAlignedVersion() >= MacosVersion(10, 13, 4);
 #else
       false;
 #endif
@@ -859,7 +845,7 @@
   if (!&dyldVersionNumber) return true;
   // If running on OS X 10.11+ or iOS 9.0+, dyld will interpose even if
   // DYLD_INSERT_LIBRARIES is not set. However, checking OS version via
-  // GetMacosVersion() doesn't work for the simulator. Let's instead check
+  // GetMacosAlignedVersion() doesn't work for the simulator. Let's instead check
   // `dyldVersionNumber`, which is exported by dyld, against a known version
   // number from the first OS release where this appeared.
   return dyldVersionNumber < kMinDyldVersionWithAutoInterposition;
diff --git a/compiler-rt/lib/sanitizer_common/sanitizer_malloc_mac.inc b/compiler-rt/lib/sanitizer_common/sanitizer_malloc_mac.inc
--- a/compiler-rt/lib/sanitizer_common/sanitizer_malloc_mac.inc
+++ b/compiler-rt/lib/sanitizer_common/sanitizer_malloc_mac.inc
@@ -61,7 +61,7 @@
   malloc_zone_t *new_zone = (malloc_zone_t *)p;
   internal_memcpy(new_zone, &sanitizer_zone, sizeof(sanitizer_zone));
   new_zone->zone_name = NULL;  // The name will be changed anyway.
-  if (GetMacosVersion() >= MACOS_VERSION_LION) {
+  if (GetMacosAlignedVersion() >= MacosVersion(10, 7)) {
     // Prevent the client app from overwriting the zone contents.
     // Library functions that need to modify the zone will set PROT_WRITE on it.
     // This matches the behavior of malloc_create_zone() on OSX 10.7 and higher.
@@ -75,7 +75,7 @@
   COMMON_MALLOC_ENTER();
   // We don't need to do anything here.  We're not registering new zones, so we
   // don't to unregister.  Just un-mprotect and free() the zone.
-  if (GetMacosVersion() >= MACOS_VERSION_LION) {
+  if (GetMacosAlignedVersion() >= MacosVersion(10, 7)) {
     uptr page_size = GetPageSizeCached();
     uptr allocated_size = RoundUpTo(sizeof(sanitizer_zone), page_size);
     mprotect(zone, allocated_size, PROT_READ | PROT_WRITE);
diff --git a/compiler-rt/lib/sanitizer_common/sanitizer_symbolizer_mac.cpp b/compiler-rt/lib/sanitizer_common/sanitizer_symbolizer_mac.cpp
--- a/compiler-rt/lib/sanitizer_common/sanitizer_symbolizer_mac.cpp
+++ b/compiler-rt/lib/sanitizer_common/sanitizer_symbolizer_mac.cpp
@@ -123,7 +123,7 @@
     argv[i++] = path_to_binary;
     argv[i++] = "-p";
     argv[i++] = &pid_str_[0];
-    if (GetMacosVersion() == MACOS_VERSION_MAVERICKS) {
+    if (GetMacosAlignedVersion() == MacosVersion(10, 9)) {
       // On Mavericks atos prints a deprecation warning which we suppress by
       // passing -d. The warning isn't present on other OSX versions, even the
       // newer ones.
diff --git a/compiler-rt/lib/tsan/rtl/tsan_platform_mac.cpp b/compiler-rt/lib/tsan/rtl/tsan_platform_mac.cpp
--- a/compiler-rt/lib/tsan/rtl/tsan_platform_mac.cpp
+++ b/compiler-rt/lib/tsan/rtl/tsan_platform_mac.cpp
@@ -261,7 +261,7 @@
       pthread_introspection_hook_install(&my_pthread_introspection_hook);
 #endif
 
-  if (GetMacosVersion() >= MACOS_VERSION_MOJAVE) {
+  if (GetMacosAlignedVersion() >= MacosVersion(10, 14)) {
     // Libsystem currently uses a process-global key; this might change.
     const unsigned kTLSLongjmpXorKeySlot = 0x7;
     longjmp_xor_key = (uptr)pthread_getspecific(kTLSLongjmpXorKeySlot);
@@ -270,7 +270,7 @@
 
 #ifdef __aarch64__
 # define LONG_JMP_SP_ENV_SLOT \
-    ((GetMacosVersion() >= MACOS_VERSION_MOJAVE) ? 12 : 13)
+    ((GetMacosAlignedVersion() >= MacosVersion(10, 14)) ? 12 : 13)
 #else
 # define LONG_JMP_SP_ENV_SLOT 2
 #endif