diff --git a/clang-tools-extra/test/clang-apply-replacements/Inputs/crlf/crlf.cpp b/clang-tools-extra/test/clang-apply-replacements/Inputs/crlf/crlf.cpp
--- a/clang-tools-extra/test/clang-apply-replacements/Inputs/crlf/crlf.cpp
+++ b/clang-tools-extra/test/clang-apply-replacements/Inputs/crlf/crlf.cpp
@@ -1,6 +1,6 @@
-
-// This file intentionally uses a CRLF newlines!
-
-void foo() {
-  int *x = 0;
-}
+
+// This file intentionally uses a CRLF newlines!
+
+void foo() {
+  int *x = 0;
+}
diff --git a/clang-tools-extra/test/clang-apply-replacements/Inputs/crlf/crlf.cpp.expected b/clang-tools-extra/test/clang-apply-replacements/Inputs/crlf/crlf.cpp.expected
--- a/clang-tools-extra/test/clang-apply-replacements/Inputs/crlf/crlf.cpp.expected
+++ b/clang-tools-extra/test/clang-apply-replacements/Inputs/crlf/crlf.cpp.expected
@@ -1,6 +1,6 @@
-
-// This file intentionally uses a CRLF newlines!
-
-void foo() {
-  int *x = nullptr;
-}
+
+// This file intentionally uses a CRLF newlines!
+
+void foo() {
+  int *x = nullptr;
+}
diff --git a/clang/include/clang/Basic/DiagnosticLexKinds.td b/clang/include/clang/Basic/DiagnosticLexKinds.td
--- a/clang/include/clang/Basic/DiagnosticLexKinds.td
+++ b/clang/include/clang/Basic/DiagnosticLexKinds.td
@@ -427,6 +427,8 @@
 def ext_pp_opencl_variadic_macros : Extension<
   "variadic macros are a Clang extension in OpenCL">;
 
+def warn_pp_gnu_ext_line_directive : Warning<"style of line directive is a GNU extension">;
+
 def err_pp_invalid_directive : Error<"invalid preprocessing directive">;
 def err_pp_directive_required : Error<
   "%0 must be used within a preprocessing directive">;
diff --git a/clang/lib/Lex/PPDirectives.cpp b/clang/lib/Lex/PPDirectives.cpp
--- a/clang/lib/Lex/PPDirectives.cpp
+++ b/clang/lib/Lex/PPDirectives.cpp
@@ -1432,6 +1432,7 @@
   // string followed by eod.
   if (StrTok.is(tok::eod)) {
     // Treat this like "#line NN", which doesn't change file characteristics.
+    Diag(StrTok, diag::warn_pp_gnu_ext_line_directive);
     FileKind = SourceMgr.getFileCharacteristic(DigitTok.getLocation());
   } else if (StrTok.isNot(tok::string_literal)) {
     Diag(StrTok, diag::err_pp_linemarker_invalid_filename);
diff --git a/clang/test/Misc/warning-flags.c b/clang/test/Misc/warning-flags.c
--- a/clang/test/Misc/warning-flags.c
+++ b/clang/test/Misc/warning-flags.c
@@ -18,7 +18,7 @@
 
 The list of warnings below should NEVER grow.  It should gradually shrink to 0.
 
-CHECK: Warnings without flags (67):
+CHECK: Warnings without flags (68):
 
 CHECK-NEXT:   ext_expected_semi_decl_list
 CHECK-NEXT:   ext_explicit_specialization_storage_class
@@ -71,6 +71,7 @@
 CHECK-NEXT:   warn_on_superclass_use
 CHECK-NEXT:   warn_pp_convert_to_positive
 CHECK-NEXT:   warn_pp_expr_overflow
+CHECK-NEXT:   warn_pp_gnu_ext_line_directive
 CHECK-NEXT:   warn_pp_line_decimal
 CHECK-NEXT:   warn_pragma_pack_pop_identifier_and_alignment
 CHECK-NEXT:   warn_pragma_pack_show
diff --git a/clang/test/Preprocessor/line-directive.c b/clang/test/Preprocessor/line-directive.c
--- a/clang/test/Preprocessor/line-directive.c
+++ b/clang/test/Preprocessor/line-directive.c
@@ -27,7 +27,7 @@
 #define A 42 "foo"
 #line A
 
-# 42
+# 42 // expected-warning {{style of line directive is a GNU extension}}
 # 42 "foo"
 # 42 "foo" 2 // expected-error {{invalid line marker flag '2': cannot pop empty include stack}}
 # 42 "foo" 1 3  // enter
@@ -97,7 +97,7 @@
 #line 010  // expected-warning {{#line directive interprets number as decimal, not octal}}
 extern int array[__LINE__ == 10 ? 1:-1];
 
-# 020      // expected-warning {{GNU line marker directive interprets number as decimal, not octal}}
+# 020      // expected-warning {{GNU line marker directive interprets number as decimal, not octal}} expected-warning {{style of line directive is a GNU extension}}
 extern int array_gnuline[__LINE__ == 20 ? 1:-1];
 
 /* PR3917 */
@@ -106,7 +106,7 @@
 _\
 _LINE__ == 42 ? 1: -1];  /* line marker is location of first _ */
 
-# 51
+# 51 // expected-warning {{style of line directive is a GNU extension}}
 extern char array2_gnuline[\
 _\
 _LINE__ == 52 ? 1: -1];  /* line marker is location of first _ */
diff --git a/clang/test/Preprocessor/warn-gnu-ext-line-directive.c b/clang/test/Preprocessor/warn-gnu-ext-line-directive.c
new file mode 100644
--- /dev/null
+++ b/clang/test/Preprocessor/warn-gnu-ext-line-directive.c
@@ -0,0 +1,3 @@
+// RUN: %clang_cc1 -fsyntax-only %s -verify
+
+#1 // expected-warning {{style of line directive is a GNU extension}}