diff --git a/newlib/libc/include/ctype.h b/newlib/libc/include/ctype.h
index 1cee6953b..a0009af17 100644
--- a/newlib/libc/include/ctype.h
+++ b/newlib/libc/include/ctype.h
@@ -5,7 +5,7 @@
 #include <sys/cdefs.h>
 
 #if __POSIX_VISIBLE >= 200809 || __MISC_VISIBLE || defined (_COMPILING_NEWLIB)
-#include <xlocale.h>
+#include <sys/_locale.h>
 #endif
 
 _BEGIN_STD_C
diff --git a/newlib/libc/include/inttypes.h b/newlib/libc/include/inttypes.h
index 694ba8fcf..073215476 100644
--- a/newlib/libc/include/inttypes.h
+++ b/newlib/libc/include/inttypes.h
@@ -22,7 +22,7 @@
 #include <stddef.h>
 
 #if __BSD_VISIBLE
-#include <xlocale.h>
+#include <sys/_locale.h>
 #endif
 
 #define __STRINGIFY(a) #a
diff --git a/newlib/libc/include/langinfo.h b/newlib/libc/include/langinfo.h
index d2b7a031c..fcf986cce 100644
--- a/newlib/libc/include/langinfo.h
+++ b/newlib/libc/include/langinfo.h
@@ -32,7 +32,7 @@
 #include <sys/cdefs.h>
 #include <sys/_types.h>
 #if __POSIX_VISIBLE >= 200809
-#include <xlocale.h>
+#include <sys/_locale.h>
 #endif
 
 #ifndef _NL_ITEM_DECLARED
diff --git a/newlib/libc/include/locale.h b/newlib/libc/include/locale.h
index d11eb00fb..8abb8db92 100644
--- a/newlib/libc/include/locale.h
+++ b/newlib/libc/include/locale.h
@@ -23,7 +23,7 @@
 
 #if __POSIX_VISIBLE >= 200809 || defined (_COMPILING_NEWLIB)
 
-#include <xlocale.h>
+#include <sys/_locale.h>
 
 #define LC_ALL_MASK		(1 << LC_ALL)
 #define LC_COLLATE_MASK		(1 << LC_COLLATE)
diff --git a/newlib/libc/include/stdlib.h b/newlib/libc/include/stdlib.h
index 933d181e1..15b349440 100644
--- a/newlib/libc/include/stdlib.h
+++ b/newlib/libc/include/stdlib.h
@@ -27,7 +27,7 @@
 #endif
 
 #if __GNU_VISIBLE
-#include <xlocale.h>
+#include <sys/_locale.h>
 #endif
 
 _BEGIN_STD_C
diff --git a/newlib/libc/include/string.h b/newlib/libc/include/string.h
index 04c4d1828..60e837bc0 100644
--- a/newlib/libc/include/string.h
+++ b/newlib/libc/include/string.h
@@ -17,7 +17,7 @@
 #include <stddef.h>
 
 #if __POSIX_VISIBLE >= 200809
-#include <xlocale.h>
+#include <sys/_locale.h>
 #endif
 
 #if __BSD_VISIBLE
diff --git a/newlib/libc/include/strings.h b/newlib/libc/include/strings.h
index 7e2e557e7..f0f7ee137 100644
--- a/newlib/libc/include/strings.h
+++ b/newlib/libc/include/strings.h
@@ -33,7 +33,7 @@
 #include <sys/_types.h>
 
 #if __POSIX_VISIBLE >= 200809
-#include <xlocale.h>
+#include <sys/_locale.h>
 #endif
 
 #ifndef _SIZE_T_DECLARED
diff --git a/newlib/libc/include/xlocale.h b/newlib/libc/include/sys/_locale.h
similarity index 70%
rename from newlib/libc/include/xlocale.h
rename to newlib/libc/include/sys/_locale.h
index f9554269c..ce6f9955c 100644
--- a/newlib/libc/include/xlocale.h
+++ b/newlib/libc/include/sys/_locale.h
@@ -1,7 +1,7 @@
 /* Definition of opaque POSIX-1.2008 type locale_t for userspace. */
 
-#ifndef	_XLOCALE_H
-#define _XLOCALE_H
+#ifndef	_SYS__LOCALE_H
+#define _SYS__LOCALE_H
 
 #include <newlib.h>
 #include <sys/config.h>
@@ -9,4 +9,4 @@
 struct __locale_t;
 typedef struct __locale_t *locale_t;
 
-#endif	/* _XLOCALE_H */
+#endif	/* _SYS__LOCALE_H */
diff --git a/newlib/libc/include/time.h b/newlib/libc/include/time.h
index d69d19969..3031590b4 100644
--- a/newlib/libc/include/time.h
+++ b/newlib/libc/include/time.h
@@ -29,7 +29,7 @@
 #include <sys/timespec.h>
 
 #if __POSIX_VISIBLE >= 200809
-#include <xlocale.h>
+#include <sys/_locale.h>
 #endif
 
 _BEGIN_STD_C
diff --git a/newlib/libc/include/wchar.h b/newlib/libc/include/wchar.h
index 9f2441c4f..c04a6510e 100644
--- a/newlib/libc/include/wchar.h
+++ b/newlib/libc/include/wchar.h
@@ -64,7 +64,7 @@ typedef __gnuc_va_list va_list;
 #endif
 
 #if __POSIX_VISIBLE >= 200809
-#include <xlocale.h>
+#include <sys/_locale.h>
 #endif
 
 _BEGIN_STD_C
diff --git a/newlib/libc/include/wctype.h b/newlib/libc/include/wctype.h
index 9b710900d..e5452bfc3 100644
--- a/newlib/libc/include/wctype.h
+++ b/newlib/libc/include/wctype.h
@@ -8,7 +8,7 @@
 #include <stddef.h>
 
 #if __POSIX_VISIBLE >= 200809
-#include <xlocale.h>
+#include <sys/_locale.h>
 #endif
 
 #ifndef WEOF
diff --git a/winsup/cygwin/include/monetary.h b/winsup/cygwin/include/monetary.h
index 82a6312bf..1c3479bd8 100644
--- a/winsup/cygwin/include/monetary.h
+++ b/winsup/cygwin/include/monetary.h
@@ -32,7 +32,7 @@
 #include <sys/cdefs.h>
 #include <sys/types.h>
 #if __POSIX_VISIBLE >= 200809
-#include <xlocale.h>
+#include <sys/_locale.h>
 #endif
 
 __BEGIN_DECLS
diff --git a/winsup/cygwin/release/3.1.0 b/winsup/cygwin/release/3.1.0
index fe65e5082..bdbbf092d 100644
--- a/winsup/cygwin/release/3.1.0
+++ b/winsup/cygwin/release/3.1.0
@@ -16,6 +16,9 @@ What changed:
 - If a SA_SIGINFO signal handler changes the ucontext_t pointed to by
   the third parameter, follow it after returning from the handler.
 
+- Eliminate a header file name collision with <X11/XLocale.h> on case
+  insensitive filesystems by reverting <xlocale.h> back to <sys/_locale.h>.
+
 
 Bug Fixes
 ---------
diff --git a/winsup/doc/new-features.xml b/winsup/doc/new-features.xml
index 1ce011e3b..49aa5da74 100644
--- a/winsup/doc/new-features.xml
+++ b/winsup/doc/new-features.xml
@@ -8,6 +8,12 @@
 
 <itemizedlist mark="bullet">
 
+<listitem><para>
+Eliminate a header file name collision with &lt;X11/XLocale.h&gt; on
+case insensitive filesystems by reverting &lt;xlocale.h&gt; back to
+&lt;sys/_locale.h&gt;.
+</para></listitem>
+
 <listitem><para>
 FIFOs can now be opened multiple times for writing.
 </para></listitem>