diff --git a/lib/Support/Unix/Host.inc b/lib/Support/Unix/Host.inc
index 744fb9e6996..c5de97f73c9 100644
--- a/lib/Support/Unix/Host.inc
+++ b/lib/Support/Unix/Host.inc
@@ -30,7 +30,9 @@ static std::string getOSVersion() {
   struct utsname info;
 
 #ifdef __APPLE__
-  // Recognize UNAME_RELEASE environment variable to match Darwin uname.
+  // Recognize UNAME_RELEASE environment variable to match Darwin's uname,
+  // where the value of this variable sets the OS release version
+  // reported by "uname -r".
   const char *UnameOverride = ::getenv("UNAME_RELEASE");
   if (UnameOverride && UnameOverride[0] != '\0')
     return UnameOverride;