diff --git a/U_Check-for-NULL-strings-before-getting-their-lengths.patch b/U_Check-for-NULL-strings-before-getting-their-lengths.patch
new file mode 100644
index 0000000..ae91bf9
--- /dev/null
+++ b/U_Check-for-NULL-strings-before-getting-their-lengths.patch
@@ -0,0 +1,160 @@
+From ab2f59530b16bdfbf023b8e025c7c8aba3b6fd0c Mon Sep 17 00:00:00 2001
+From: Matthieu Herrb <matthieu@herrb.eu>
+Date: Sun, 30 May 2021 16:33:48 +0200
+Subject: [PATCH] Check for NULL strings before getting their lengths
+
+Problem reported by Karsten Trulsen
+
+Signed-off-by: Matthieu Herrb <matthieu@herrb.eu>
+---
+ src/Font.c      | 2 +-
+ src/FontInfo.c  | 2 +-
+ src/FontNames.c | 2 +-
+ src/GetColor.c  | 2 +-
+ src/LoadFont.c  | 2 +-
+ src/LookupCol.c | 2 ++
+ src/ParseCol.c  | 2 +-
+ src/QuExt.c     | 2 +-
+ src/StNColor.c  | 2 +-
+ src/StName.c    | 4 ++--
+ 10 files changed, 12 insertions(+), 10 deletions(-)
+
+Index: libX11-1.7.1/src/Font.c
+===================================================================
+--- libX11-1.7.1.orig/src/Font.c
++++ libX11-1.7.1/src/Font.c
+@@ -102,7 +102,7 @@ XFontStruct *XLoadQueryFont(
+     XF86BigfontCodes *extcodes = _XF86BigfontCodes(dpy);
+ #endif
+ 
+-    if (strlen(name) >= USHRT_MAX)
++    if (name != NULL && strlen(name) >= USHRT_MAX)
+         return NULL;
+     if (_XF86LoadQueryLocaleFont(dpy, name, &font_result, (Font *)0))
+       return font_result;
+Index: libX11-1.7.1/src/FontInfo.c
+===================================================================
+--- libX11-1.7.1.orig/src/FontInfo.c
++++ libX11-1.7.1/src/FontInfo.c
+@@ -58,7 +58,7 @@ XFontStruct **info)	/* RETURN */
+     register xListFontsReq *req;
+     int j;
+ 
+-    if (strlen(pattern) >= USHRT_MAX)
++    if (pattern != NULL && strlen(pattern) >= USHRT_MAX)
+         return NULL;
+ 
+     LockDisplay(dpy);
+Index: libX11-1.7.1/src/FontNames.c
+===================================================================
+--- libX11-1.7.1.orig/src/FontNames.c
++++ libX11-1.7.1/src/FontNames.c
+@@ -51,7 +51,7 @@ int *actualCount)	/* RETURN */
+     register xListFontsReq *req;
+     unsigned long rlen = 0;
+ 
+-    if (strlen(pattern) >= USHRT_MAX)
++    if (pattern != NULL && strlen(pattern) >= USHRT_MAX)
+         return NULL;
+ 
+     LockDisplay(dpy);
+Index: libX11-1.7.1/src/GetColor.c
+===================================================================
+--- libX11-1.7.1.orig/src/GetColor.c
++++ libX11-1.7.1/src/GetColor.c
+@@ -49,7 +49,7 @@ XColor *exact_def) /* RETURN */
+     XcmsColor cmsColor_exact;
+     Status ret;
+ 
+-    if (strlen(colorname) >= USHRT_MAX)
++    if (colorname != NULL && strlen(colorname) >= USHRT_MAX)
+         return (0);
+ 
+ #ifdef XCMS
+Index: libX11-1.7.1/src/LoadFont.c
+===================================================================
+--- libX11-1.7.1.orig/src/LoadFont.c
++++ libX11-1.7.1/src/LoadFont.c
+@@ -39,7 +39,7 @@ XLoadFont (
+     Font fid;
+     register xOpenFontReq *req;
+ 
+-    if (strlen(name) >= USHRT_MAX)
++    if (name != NULL && strlen(name) >= USHRT_MAX)
+         return (0);
+ 
+     if (_XF86LoadQueryLocaleFont(dpy, name, (XFontStruct **)0, &fid))
+Index: libX11-1.7.1/src/LookupCol.c
+===================================================================
+--- libX11-1.7.1.orig/src/LookupCol.c
++++ libX11-1.7.1/src/LookupCol.c
+@@ -47,6 +47,8 @@ XLookupColor (
+ 	XcmsCCC ccc;
+ 	XcmsColor cmsColor_exact;
+ 
++	if (spec == NULL)
++		return 0;
+ 	n = (int) strlen (spec);
+ 	if (n >= USHRT_MAX)
+             return 0;
+Index: libX11-1.7.1/src/ParseCol.c
+===================================================================
+--- libX11-1.7.1.orig/src/ParseCol.c
++++ libX11-1.7.1/src/ParseCol.c
+@@ -46,7 +46,7 @@ XParseColor (
+ 	XcmsCCC ccc;
+ 	XcmsColor cmsColor;
+ 
+-        if (!spec) return(0);
++	if (!spec) return(0);
+ 	n = (int) strlen (spec);
+ 	if (n >= USHRT_MAX)
+             return(0);
+Index: libX11-1.7.1/src/QuExt.c
+===================================================================
+--- libX11-1.7.1.orig/src/QuExt.c
++++ libX11-1.7.1/src/QuExt.c
+@@ -42,7 +42,7 @@ XQueryExtension(
+     xQueryExtensionReply rep;
+     register xQueryExtensionReq *req;
+ 
+-    if (strlen(name) >= USHRT_MAX)
++    if (name != NULL && strlen(name) >= USHRT_MAX)
+         return false;
+ 
+     if (name && strlen (name) < 256)
+Index: libX11-1.7.1/src/StNColor.c
+===================================================================
+--- libX11-1.7.1.orig/src/StNColor.c
++++ libX11-1.7.1/src/StNColor.c
+@@ -47,7 +47,7 @@ int flags)  /* DoRed, DoGreen, DoBlue */
+     XcmsColor cmsColor_exact;
+     XColor scr_def;
+ 
+-    if (strlen(name) >= USHRT_MAX)
++    if (name != NULL && strlen(name) >= USHRT_MAX)
+         return 0;
+ #ifdef XCMS
+     /*
+Index: libX11-1.7.1/src/StName.c
+===================================================================
+--- libX11-1.7.1.orig/src/StName.c
++++ libX11-1.7.1/src/StName.c
+@@ -37,7 +37,7 @@ XStoreName (
+     Window w,
+     _Xconst char *name)
+ {
+-    if (strlen(name) >= USHRT_MAX)
++    if (name != NULL && strlen(name) >= USHRT_MAX)
+         return 0;
+     return XChangeProperty(dpy, w, XA_WM_NAME, XA_STRING, /*  */
+ 			   8, PropModeReplace, (_Xconst unsigned char *)name,
+@@ -50,7 +50,7 @@ XSetIconName (
+     Window w,
+     _Xconst char *icon_name)
+ {
+-    if (strlen(icon_name) >= USHRT_MAX)
++    if (icon_name != NULL && strlen(icon_name) >= USHRT_MAX)
+         return 0;
+     return XChangeProperty(dpy, w, XA_WM_ICON_NAME, XA_STRING, 8,
+                            PropModeReplace, (_Xconst unsigned char *)icon_name,
diff --git a/libX11.changes b/libX11.changes
index b829158..39d4118 100644
--- a/libX11.changes
+++ b/libX11.changes
@@ -1,3 +1,10 @@
+-------------------------------------------------------------------
+Mon May 31 15:33:38 UTC 2021 - Stefan Dirsch <sndirsch@suse.com>
+
+- U_Check-for-NULL-strings-before-getting-their-lengths.patch
+  * regression in libX11 1.7.1 (boo#1186643)
+    fixes segfaults for xforms applications like fdesign
+
 -------------------------------------------------------------------
 Tue May 18 15:57:02 UTC 2021 - Stefan Dirsch <sndirsch@suse.com>
 
diff --git a/libX11.spec b/libX11.spec
index 0de73b5..e6d08df 100644
--- a/libX11.spec
+++ b/libX11.spec
@@ -33,6 +33,7 @@ Patch0:         p_khmer-compose.diff
 Patch1:         p_xlib_skip_ext_env.diff
 # PATCH-FIX-UPSTREAM en-locales.diff fdo#48596 bnc#388711 -- Add missing data for more en locales
 Patch2:         en-locales.diff
+Patch3:         U_Check-for-NULL-strings-before-getting-their-lengths.patch
 
 BuildRequires:  fdupes
 BuildRequires:  libtool
@@ -137,6 +138,7 @@ test -f nls/ja.S90/XLC_LOCALE.pre && exit 1
 %patch0
 %patch1
 %patch2
+%patch3 -p1
 
 %build
 %configure \