diff --git a/clang/include/clang/Basic/IdentifierTable.h b/clang/include/clang/Basic/IdentifierTable.h
index 9e80c3fb7079d..d0640ee34de75 100644
--- a/clang/include/clang/Basic/IdentifierTable.h
+++ b/clang/include/clang/Basic/IdentifierTable.h
@@ -74,15 +74,20 @@ enum TokenKey : unsigned {
   KEYSYCL = 0x800000,
   KEYCUDA = 0x1000000,
   KEYZOS = 0x2000000,
-  KEYNOZOS = 0x4000000,
+  // 0x4000000 was KEYNOZOS, which was unused. The value is kept reserved
+  // so that KEYALL's bit-mask computation remains correct: keywords like
+  // 'volatile' (KEYALL|KEYNOHLSL) go through the per-bit loop in
+  // getKeywordStatus, and every bit set in KEYALL must map to a valid
+  // TokenKey with a handler in getKeywordStatusHelper.
   KEYHLSL = 0x8000000,
   KEYFIXEDPOINT = 0x10000000,
   KEYDEFERTS = 0x20000000,
   KEYNOHLSL = 0x40000000,
   KEYMAX = KEYNOHLSL, // The maximum key
   KEYALLCXX = KEYCXX | KEYCXX11 | KEYCXX20,
-  KEYALL = (KEYMAX | (KEYMAX - 1)) & ~KEYNOMS18 & ~KEYNOOPENCL & ~KEYNOZOS &
-           ~KEYNOHLSL // KEYNOMS18, KEYNOOPENCL, KEYNOZOS, KEYNOHLSL excluded.
+  KEYALL = (KEYMAX | (KEYMAX - 1)) & ~KEYNOMS18 & ~KEYNOOPENCL & ~0x4000000u &
+           ~KEYNOHLSL // KEYNOMS18, KEYNOOPENCL, 0x4000000 (reserved),
+                      // KEYNOHLSL excluded.
 };
 
 /// How a keyword is treated in the selected standard. This enum is ordered
diff --git a/clang/lib/Basic/IdentifierTable.cpp b/clang/lib/Basic/IdentifierTable.cpp
index a2e9316e4e372..68cd02a623351 100644
--- a/clang/lib/Basic/IdentifierTable.cpp
+++ b/clang/lib/Basic/IdentifierTable.cpp
@@ -159,7 +159,6 @@ static KeywordStatus getKeywordStatusHelper(const LangOptions &LangOpts,
     return LangOpts.CPlusPlus ? KS_Unknown : KS_Enabled;
   case KEYNOOPENCL:
   case KEYNOMS18:
-  case KEYNOZOS:
   case KEYNOHLSL:
     // The disable behavior for this is handled in getKeywordStatus.
     return KS_Unknown;
@@ -184,8 +183,6 @@ KeywordStatus clang::getKeywordStatus(const LangOptions &LangOpts,
   if (LangOpts.MSVCCompat && (Flags & KEYNOMS18) &&
       !LangOpts.isCompatibleWithMSVC(LangOptions::MSVC2015))
     return KS_Disabled;
-  if (LangOpts.ZOSExt && (Flags & KEYNOZOS))
-    return KS_Disabled;
   KeywordStatus CurStatus = KS_Unknown;
 
   while (Flags != 0) {