diff --git a/gcc/c-family/c-opts.cc b/gcc/c-family/c-opts.cc
index fbabd1816c18cf678018e46fec139809883504c4..10403c03bd6e902cd97eddef463a8743a6378e0d 100644
--- a/gcc/c-family/c-opts.cc
+++ b/gcc/c-family/c-opts.cc
@@ -1174,6 +1174,9 @@ c_common_post_options (const char **pfilename)
 		       "the %qs debug info cannot be used with "
 		       "pre-compiled headers",
 		       debug_set_names (write_symbols & ~DWARF2_DEBUG));
+	  /* Let libcpp know that the main file is a header so it won't
+	     complain about things like #include_next and #pragma once.  */
+	  cpp_opts->main_search = CMS_header;
 	}
       else if (write_symbols != NO_DEBUG && write_symbols != DWARF2_DEBUG)
 	c_common_no_more_pch ();
diff --git a/gcc/testsuite/g++.dg/pch/main-file-warnings.C b/gcc/testsuite/g++.dg/pch/main-file-warnings.C
new file mode 100644
index 0000000000000000000000000000000000000000..a9e8b0ba9f2ca54eb6486731990aae9799ec8da2
--- /dev/null
+++ b/gcc/testsuite/g++.dg/pch/main-file-warnings.C
@@ -0,0 +1,7 @@
+/* PR pch/9471 */
+/* PR pch/47857 */
+/* Test will fail if any warnings get issued while compiling the header into a PCH.  */
+#include "main-file-warnings.H"
+#pragma once /* { dg-warning "in main file" } */
+#pragma GCC system_header /* { dg-warning "outside include file" } */
+#include_next <stdint.h> /* { dg-warning "in primary source file" } */
diff --git a/gcc/testsuite/g++.dg/pch/main-file-warnings.Hs b/gcc/testsuite/g++.dg/pch/main-file-warnings.Hs
new file mode 100644
index 0000000000000000000000000000000000000000..d1582bb8290cc039a9494cde59d78fc1c80b6caf
--- /dev/null
+++ b/gcc/testsuite/g++.dg/pch/main-file-warnings.Hs
@@ -0,0 +1,3 @@
+#pragma once /* { dg-bogus "in main file" } */
+#pragma GCC system_header /* { dg-bogus "outside include file" } */
+#include_next <stdint.h> /* { dg-bogus "in primary source file" } */
diff --git a/gcc/testsuite/gcc.dg/pch/main-file-warnings.c b/gcc/testsuite/gcc.dg/pch/main-file-warnings.c
new file mode 100644
index 0000000000000000000000000000000000000000..aedbc15f7ba73adfa55028de2995f7cb232cc1d5
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/pch/main-file-warnings.c
@@ -0,0 +1,7 @@
+/* PR pch/9471 */
+/* PR pch/47857 */
+/* Test will fail if any warnings get issued while compiling the header into a PCH.  */
+#include "main-file-warnings.h"
+#pragma once /* { dg-warning "in main file" } */
+#pragma GCC system_header /* { dg-warning "outside include file" } */
+#include_next <stdint.h> /* { dg-warning "in primary source file" } */
diff --git a/gcc/testsuite/gcc.dg/pch/main-file-warnings.hs b/gcc/testsuite/gcc.dg/pch/main-file-warnings.hs
new file mode 100644
index 0000000000000000000000000000000000000000..d1582bb8290cc039a9494cde59d78fc1c80b6caf
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/pch/main-file-warnings.hs
@@ -0,0 +1,3 @@
+#pragma once /* { dg-bogus "in main file" } */
+#pragma GCC system_header /* { dg-bogus "outside include file" } */
+#include_next <stdint.h> /* { dg-bogus "in primary source file" } */