diff --git a/libX11.changes b/libX11.changes
index 13c0073..7e58644 100644
--- a/libX11.changes
+++ b/libX11.changes
@@ -1,3 +1,9 @@
+-------------------------------------------------------------------
+Thu Mar 15 09:01:19 UTC 2018 - msrb@suse.com
+
+- u_Use-flexible-array-member-instead-of-fake-size.patch
+  * Fixes build error with gcc8. (bnc#1084639)
+
 -------------------------------------------------------------------
 Wed Mar  1 13:48:43 UTC 2017 - tobias.johannes.klausmann@mni.thm.de
 
diff --git a/libX11.spec b/libX11.spec
index f379307..48f4111 100644
--- a/libX11.spec
+++ b/libX11.spec
@@ -1,7 +1,7 @@
 #
 # spec file for package libX11
 #
-# Copyright (c) 2017 SUSE LINUX GmbH, Nuernberg, Germany.
+# Copyright (c) 2018 SUSE LINUX GmbH, Nuernberg, Germany.
 #
 # All modifications and additions to the file contributed by third parties
 # remain the property of their copyright owners, unless otherwise agreed
@@ -34,6 +34,8 @@ Patch7:         p_khmer-compose.diff
 Patch9:         p_xlib_skip_ext_env.diff
 # PATCH-FIX-UPSTREAM en-locales.diff fdo#48596 bnc#388711 -- Add missing data for more en locales
 Patch15:        en-locales.diff
+# PATCH-FIX-UPSTREAM u_Use-flexible-array-member-instead-of-fake-size.patch -- Fix build error with gcc8.
+Patch16:        u_Use-flexible-array-member-instead-of-fake-size.patch
 
 BuildRoot:      %{_tmppath}/%{name}-%{version}-build
 BuildRequires:  autoconf >= 2.60
@@ -142,6 +144,7 @@ test -f nls/ja.S90/XLC_LOCALE.pre && exit 1
 %patch7 -p0
 %patch9 -p0
 %patch15 -p0
+%patch16 -p1
 
 %build
 # Got patches which change auto*files
diff --git a/u_Use-flexible-array-member-instead-of-fake-size.patch b/u_Use-flexible-array-member-instead-of-fake-size.patch
new file mode 100644
index 0000000..028a038
--- /dev/null
+++ b/u_Use-flexible-array-member-instead-of-fake-size.patch
@@ -0,0 +1,63 @@
+Author: Michal Srb <msrb@suse.com>
+Subject: Use flexible array member instead of fake size.
+Patch-mainline: To be upstreamed
+References: bnc#1084639
+
+The _XimCacheStruct structure is followed in memory by two strings containing
+fname and encoding. The memory was accessed using the last member of the
+structure `char fname[1]`. That is a lie, prohibits us from using sizeof and
+confuses checkers. Lets declare it properly as a flexible array, so compilers
+don't complain about writing past that array. As bonus we can replace the
+XOffsetOf with regular sizeof.
+
+Fixes GCC8 error:
+  In function 'strcpy',
+      inlined from '_XimWriteCachedDefaultTree' at imLcIm.c:479:5,
+      inlined from '_XimCreateDefaultTree' at imLcIm.c:616:2,
+      inlined from '_XimLocalOpenIM' at imLcIm.c:700:5:
+  /usr/include/bits/string_fortified.h:90:10: error: '__builtin_strcpy'
+  forming offset 2 is out of the bounds [0, 1] [-Werror=array-bounds]
+     return __builtin___strcpy_chk (__dest, __src, __bos (__dest));
+
+Caused by this line seemingly writing past the fname[1] array:
+  imLcIm.c:479:  strcpy (m->fname+strlen(name)+1, encoding);
+---
+ modules/im/ximcp/imLcIm.c | 8 ++++----
+ 1 file changed, 4 insertions(+), 4 deletions(-)
+
+diff --git a/modules/im/ximcp/imLcIm.c b/modules/im/ximcp/imLcIm.c
+index c19695df..743df77b 100644
+--- a/modules/im/ximcp/imLcIm.c
++++ b/modules/im/ximcp/imLcIm.c
+@@ -82,8 +82,8 @@ struct _XimCacheStruct {
+     DTCharIndex     mbused;
+     DTCharIndex     wcused;
+     DTCharIndex     utf8used;
+-    char            fname[1];
+-    /* char encoding[1] */
++    char            fname[];
++    /* char encoding[] */
+ };
+ 
+ static struct  _XimCacheStruct* _XimCache_mmap = NULL;
+@@ -281,7 +281,7 @@ _XimReadCachedDefaultTree(
+     assert (m->id == XIM_CACHE_MAGIC);
+     assert (m->version == XIM_CACHE_VERSION);
+     if (size != m->size ||
+-	size < XOffsetOf (struct _XimCacheStruct, fname) + namelen + encodinglen) {
++	size < sizeof (struct _XimCacheStruct) + namelen + encodinglen) {
+ 	fprintf (stderr, "Ignoring broken XimCache %s [%s]\n", name, encoding);
+         munmap (m, size);
+         return False;
+@@ -442,7 +442,7 @@ _XimWriteCachedDefaultTree(
+     int   fd;
+     FILE *fp;
+     struct _XimCacheStruct *m;
+-    int   msize = (XOffsetOf(struct _XimCacheStruct, fname)
++    int   msize = (sizeof(struct _XimCacheStruct)
+ 		   + strlen(name) + strlen(encoding) + 2
+ 		   + XIM_CACHE_TREE_ALIGNMENT-1) & -XIM_CACHE_TREE_ALIGNMENT;
+     DefTreeBase *b = &im->private.local.base;
+-- 
+2.13.6
+