diff --git a/expat/CMakeLists.txt b/expat/CMakeLists.txt
index 128966be..271ccf3b 100644
--- a/expat/CMakeLists.txt
+++ b/expat/CMakeLists.txt
@@ -22,6 +22,12 @@ option(INSTALL "install expat files in cmake install target" ON)
 set(XML_CONTEXT_BYTES 1024 CACHE STRING "Define to specify how much context to retain around the current parse point")
 option(XML_DTD "Define to make parameter entity parsing functionality available" ON)
 option(XML_NS "Define to make XML Namespaces functionality available" ON)
+if(NOT WIN32)
+    option(XML_DEV_URANDOM "Define to include code reading entropy from `/dev/urandom'." ON)
+    if(XML_DEV_URANDOM)
+        add_definitions(-DXML_DEV_URANDOM)
+    endif()
+endif()
 
 if(XML_DTD)
     set(XML_DTD 1)