diff --git a/libcpp/ChangeLog b/libcpp/ChangeLog
index 20171bc8e9e..619dfd8308a 100644
--- a/libcpp/ChangeLog
+++ b/libcpp/ChangeLog
@@ -1,3 +1,9 @@
+2014-05-09  Joey Ye  <joey.ye@arm.com>
+
+	* files.c (find_file_in_dir): Always try to shorten for DOS
+	non-system headers.
+	* init.c (ENABLE_CANONICAL_SYSTEM_HEADERS): Default enabled for DOS.
+
 2014-05-07  Richard Biener  <rguenther@suse.de>
 
 	* configure.ac: Always set need_64bit_hwint to yes.
diff --git a/libcpp/files.c b/libcpp/files.c
index 7e887785444..ad68682e99e 100644
--- a/libcpp/files.c
+++ b/libcpp/files.c
@@ -387,8 +387,14 @@ find_file_in_dir (cpp_reader *pfile, _cpp_file *file, bool *invalid_pch)
       char *copy;
       void **pp;
 
-      /* We try to canonicalize system headers.  */
-      if (CPP_OPTION (pfile, canonical_system_headers) && file->dir->sysp)
+      /* We try to canonicalize system headers.  For DOS based file
+       * system, we always try to shorten non-system headers, as DOS
+       * has a tighter constraint on max path length.  */
+      if (CPP_OPTION (pfile, canonical_system_headers) && file->dir->sysp
+#ifdef HAVE_DOS_BASED_FILE_SYSTEM
+	  || !file->dir->sysp
+#endif
+	 )
 	{
 	  char * canonical_path = maybe_shorter_path (path);
 	  if (canonical_path)
diff --git a/libcpp/init.c b/libcpp/init.c
index f10413ab3eb..b80951544d4 100644
--- a/libcpp/init.c
+++ b/libcpp/init.c
@@ -27,8 +27,12 @@ along with this program; see the file COPYING3.  If not see
 #include "filenames.h"
 
 #ifndef ENABLE_CANONICAL_SYSTEM_HEADERS
+#ifdef HAVE_DOS_BASED_FILE_SYSTEM
+#define ENABLE_CANONICAL_SYSTEM_HEADERS 1
+#else
 #define ENABLE_CANONICAL_SYSTEM_HEADERS 0
 #endif
+#endif
 
 static void init_library (void);
 static void mark_named_operators (cpp_reader *, int);