Index: clang/lib/Format/TokenAnnotator.cpp
===================================================================
--- clang/lib/Format/TokenAnnotator.cpp
+++ clang/lib/Format/TokenAnnotator.cpp
@@ -844,14 +844,15 @@
       break;
     case tok::kw_if:
     case tok::kw_while:
-      assert(!Line.startsWith(tok::hash));
-      if (Tok->is(tok::kw_if) && CurrentToken &&
-          CurrentToken->isOneOf(tok::kw_constexpr, tok::identifier))
-        next();
-      if (CurrentToken && CurrentToken->is(tok::l_paren)) {
-        next();
-        if (!parseParens(/*LookForDecls=*/true))
-          return false;
+      if (!Line.startsWith(tok::hash)) {
+        if (Tok->is(tok::kw_if) && CurrentToken &&
+            CurrentToken->isOneOf(tok::kw_constexpr, tok::identifier))
+          next();
+        if (CurrentToken && CurrentToken->is(tok::l_paren)) {
+          next();
+          if (!parseParens(/*LookForDecls=*/true))
+            return false;
+        }
       }
       break;
     case tok::kw_for:
Index: clang/unittests/Format/FormatTest.cpp
===================================================================
--- clang/unittests/Format/FormatTest.cpp
+++ clang/unittests/Format/FormatTest.cpp
@@ -14679,6 +14679,12 @@
   */
 }
 
-} // end namespace
-} // end namespace format
-} // end namespace clang
+TEST_F(FormatTest, STLWhileNotDefineChed) {
+  verifyFormat("#if defined(while)\n"
+               "#define while EMIT WARNING C4005\n"
+               "#endif // while");
+}
+
+} // namespace
+} // namespace format
+} // namespace clang