diff --git a/gcc/c-family/c-common.cc b/gcc/c-family/c-common.cc
index 655c3aefee6..6e41ceb38e9 100644
--- a/gcc/c-family/c-common.cc
+++ b/gcc/c-family/c-common.cc
@@ -284,9 +284,11 @@ int c_inhibit_evaluation_warnings;
    be generated.  */
 bool in_late_binary_op;
 
-/* Whether lexing has been completed, so subsequent preprocessor
-   errors should use the compiler's input_location.  */
-bool done_lexing = false;
+/* Depending on which phase of processing we are in, we may need
+   to prefer input_location to libcpp's locations.  (Specifically,
+   after the C++ lexer is done lexing tokens, but prior to calling
+   cpp_finish (), we need to do so.  */
+bool override_libcpp_locations;
 
 /* Information about how a function name is generated.  */
 struct fname_var_t
@@ -6681,7 +6683,7 @@ c_cpp_diagnostic (cpp_reader *pfile ATTRIBUTE_UNUSED,
     default:
       gcc_unreachable ();
     }
-  if (done_lexing)
+  if (override_libcpp_locations)
     richloc->set_range (0, input_location, SHOW_RANGE_WITH_CARET);
   diagnostic_set_info_translated (&diagnostic, msg, ap,
 				  richloc, dlevel);
diff --git a/gcc/c-family/c-common.h b/gcc/c-family/c-common.h
index f9064393b4e..c06769b6f0b 100644
--- a/gcc/c-family/c-common.h
+++ b/gcc/c-family/c-common.h
@@ -767,10 +767,12 @@ extern int max_tinst_depth;
 
 extern int c_inhibit_evaluation_warnings;
 
-/* Whether lexing has been completed, so subsequent preprocessor
-   errors should use the compiler's input_location.  */
+/* Depending on which phase of processing we are in, we may need
+   to prefer input_location to libcpp's locations.  (Specifically,
+   after the C++ lexer is done lexing tokens, but prior to calling
+   cpp_finish (), we need to do so.  */
 
-extern bool done_lexing;
+extern bool override_libcpp_locations;
 
 /* C types are partitioned into three subsets: object, function, and
    incomplete types.  */
diff --git a/gcc/c-family/c-opts.cc b/gcc/c-family/c-opts.cc
index b9f01a65ed7..4e1463689de 100644
--- a/gcc/c-family/c-opts.cc
+++ b/gcc/c-family/c-opts.cc
@@ -1281,6 +1281,12 @@ c_common_finish (void)
 	}
     }
 
+  /* When we call cpp_finish (), it may generate some diagnostics using
+     locations it remembered from the preprocessing phase, e.g. for
+     -Wunused-macros.  So inform c_cpp_diagnostic () not to override those
+     locations with input_location, which would be incorrect now.  */
+  override_libcpp_locations = false;
+
   /* For performance, avoid tearing down cpplib's internal structures
      with cpp_destroy ().  */
   cpp_finish (parse_in, deps_stream);
diff --git a/gcc/cp/parser.cc b/gcc/cp/parser.cc
index 4f67441eeb1..66e6fde3e28 100644
--- a/gcc/cp/parser.cc
+++ b/gcc/cp/parser.cc
@@ -755,7 +755,7 @@ cp_lexer_new_main (void)
 
   /* Subsequent preprocessor diagnostics should use compiler
      diagnostic functions to get the compiler source location.  */
-  done_lexing = true;
+  override_libcpp_locations = true;
 
   maybe_check_all_macros (parse_in);
 
diff --git a/gcc/testsuite/c-c++-common/pragma-diag-15.c b/gcc/testsuite/c-c++-common/pragma-diag-15.c
index d8076b4f93a..8ffff88d5e3 100644
--- a/gcc/testsuite/c-c++-common/pragma-diag-15.c
+++ b/gcc/testsuite/c-c++-common/pragma-diag-15.c
@@ -9,5 +9,5 @@
    because the location of the macro definition is incorrectly set.  This is a
    separate issue, will resolve it in a later patch.  */
 
-#define X /* { dg-warning "-:-Wunused-macros" {} { xfail c++ } } */
+#define X /* { dg-warning "-:-Wunused-macros" } */
 #pragma GCC diagnostic ignored "-Wunused-macros"