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
@@ -40,13 +40,28 @@
   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 DarwinKernelVersion {
+  u16 major;
+  u16 minor;
+
+  DarwinKernelVersion(u16 major, u16 minor) : major(major), minor(minor) {}
+
+  bool operator==(const DarwinKernelVersion &other) const {
+    return major == other.major && minor == other.minor;
+  }
+  bool operator>=(const DarwinKernelVersion &other) const {
+    return major >= other.major ||
+           (major == other.major && minor >= other.minor);
+  }
+};
+
 MacosVersion GetMacosVersion();
+DarwinKernelVersion GetDarwinKernelVersion();
 
 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
@@ -635,11 +635,7 @@
     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 17: return MACOS_VERSION_HIGH_SIERRA;
     case 18: return MACOS_VERSION_MOJAVE;
     case 19: return MACOS_VERSION_CATALINA;
     default:
@@ -660,6 +656,23 @@
   return result;
 }
 
+DarwinKernelVersion GetDarwinKernelVersion() {
+  char buf[100];
+  size_t len = sizeof(buf);
+  int res = internal_sysctlbyname("kern.osrelease", buf, &len, nullptr, 0);
+  CHECK_EQ(res, 0);
+
+  // Format: <major>.<minor>.<patch>\0
+  CHECK_GE(len, 6);
+  const char *p = buf;
+  u16 major = internal_simple_strtoll(p, &p, /*base=*/10);
+  CHECK_EQ(*p, '.');
+  p += 1;
+  u16 minor = internal_simple_strtoll(p, &p, /*base=*/10);
+
+  return DarwinKernelVersion(major, minor);
+}
+
 uptr GetRSS() {
   struct task_basic_info info;
   unsigned count = TASK_BASIC_INFO_COUNT;
@@ -796,10 +809,10 @@
 }
 
 void InitializePlatformEarly() {
-  // Only use xnu_fast_mmap when on x86_64 and the OS supports it.
+  // Only use xnu_fast_mmap when on x86_64 and the kernel supports it.
   use_xnu_fast_mmap =
 #if defined(__x86_64__)
-      GetMacosVersion() >= MACOS_VERSION_HIGH_SIERRA_DOT_RELEASE_4;
+      GetDarwinKernelVersion() >= DarwinKernelVersion(17, 5);
 #else
       false;
 #endif