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 +427,9 @@
 def ext_pp_opencl_variadic_macros : Extension<
   "variadic macros are a Clang extension in OpenCL">;
 
+def ext_pp_gnu_line_directive : Extension<
+  "this 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
@@ -1335,7 +1335,10 @@
   unsigned FlagVal;
   Token FlagTok;
   PP.Lex(FlagTok);
-  if (FlagTok.is(tok::eod)) return false;
+  if (FlagTok.is(tok::eod)) {
+    PP.Diag(FlagTok, diag::ext_pp_gnu_line_directive);
+    return false;
+  }
   if (GetLineValue(FlagTok, FlagVal, diag::err_pp_linemarker_invalid_flag, PP))
     return true;
 
@@ -1431,6 +1434,7 @@
   // If the StrTok is "eod", then it wasn't present.  Otherwise, it must be a
   // string followed by eod.
   if (StrTok.is(tok::eod)) {
+    Diag(StrTok, diag::ext_pp_gnu_line_directive);
     // Treat this like "#line NN", which doesn't change file characteristics.
     FileKind = SourceMgr.getFileCharacteristic(DigitTok.getLocation());
   } else if (StrTok.isNot(tok::string_literal)) {
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
@@ -90,4 +90,4 @@
 
 The list of warnings in -Wpedantic should NEVER grow.
 
-CHECK: Number in -Wpedantic (not covered by other -W flags): 27
+CHECK: Number in -Wpedantic (not covered by other -W flags): 28
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
@@ -27,8 +27,8 @@
 #define A 42 "foo"
 #line A
 
-# 42
-# 42 "foo"
+# 42 // expected-warning {{this style of line directive is a GNU extension}}
+# 42 "foo" // expected-warning {{this style of line directive is a GNU extension}}
 # 42 "foo" 2 // expected-error {{invalid line marker flag '2': cannot pop empty include stack}}
 # 42 "foo" 1 3  // enter
 # 42 "foo" 2 3  // exit
@@ -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 {{this 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 {{this style of line directive is a GNU extension}}
 extern char array2_gnuline[\
 _\
 _LINE__ == 52 ? 1: -1];  /* line marker is location of first _ */
@@ -115,7 +115,7 @@
 #line 0 "line-directive.c" // expected-warning {{#line directive with zero argument is a GNU extension}}
 undefined t; // expected-error {{unknown type name 'undefined'}}
 
-# 115 "main"
+# 115 "main" // expected-warning {{this style of line directive is a GNU extension}}
 # 116 "enter-1" 1
 # 117 "enter-2" 1
 # 118 "" 2 // pop to enter-1