diff --git a/gnu/local.mk b/gnu/local.mk
index ae5477c428..67d9eb703a 100644
--- a/gnu/local.mk
+++ b/gnu/local.mk
@@ -784,6 +784,7 @@ dist_patch_DATA =						\
   %D%/packages/patches/evilwm-lost-focus-bug.patch		\
   %D%/packages/patches/exiv2-CVE-2017-14860.patch		\
   %D%/packages/patches/exiv2-CVE-2017-14859-14862-14864.patch	\
+  %D%/packages/patches/expat-CVE-2018-20843.patch		\
   %D%/packages/patches/extundelete-e2fsprogs-1.44.patch		\
   %D%/packages/patches/fastcap-mulGlobal.patch			\
   %D%/packages/patches/fastcap-mulSetup.patch			\
diff --git a/gnu/packages/patches/expat-CVE-2018-20843.patch b/gnu/packages/patches/expat-CVE-2018-20843.patch
new file mode 100644
index 0000000000..216fbe9667
--- /dev/null
+++ b/gnu/packages/patches/expat-CVE-2018-20843.patch
@@ -0,0 +1,21 @@
+Fix extraction of namespace prefix from XML name.
+Fixes CVE-2018-20843
+
+This patch comes from upstream commit 11f8838bf99ea0a6f0b76f9760c43704d00c4ff6
+https://github.com/libexpat/libexpat/commit/11f8838bf99ea0a6f0b76f9760c43704d00c4ff6
+
+CVE is https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2018-20843
+
+diff --git a/expat/lib/xmlparse.c b/expat/lib/xmlparse.c
+index 30d55c5..737d7cd 100644
+--- a/lib/xmlparse.c
++++ b/lib/xmlparse.c
+@@ -6071,7 +6071,7 @@ setElementTypePrefix(XML_Parser parser, ELEMENT_TYPE *elementType)
+       else
+         poolDiscard(&dtd->pool);
+       elementType->prefix = prefix;
+-
++      break;
+     }
+   }
+   return 1;
diff --git a/gnu/packages/xml.scm b/gnu/packages/xml.scm
index e3260be103..0cd9319c95 100644
--- a/gnu/packages/xml.scm
+++ b/gnu/packages/xml.scm
@@ -66,6 +66,7 @@
 (define-public expat
   (package
     (name "expat")
+    (replacement expat/fixed)
     (version "2.2.6")
     (source (let ((dot->underscore (lambda (c) (if (char=? #\. c) #\_ c))))
               (origin
@@ -88,6 +89,14 @@ stream-oriented parser in which an application registers handlers for
 things the parser might find in the XML document (like start tags).")
     (license license:expat)))
 
+(define expat/fixed
+  (package
+    (inherit expat)
+    (source
+     (origin
+       (inherit (package-source expat))
+       (patches (search-patches "expat-CVE-2018-20843.patch"))))))
+
 (define-public libebml
   (package
     (name "libebml")