diff --git a/share/why3session.dtd b/share/why3session.dtd
index 5fa0e17441098a38a10e7b5222d6ae167b81d67b..6322dba059213ee1a3f20d8d15fb3aa915a92393 100644
--- a/share/why3session.dtd
+++ b/share/why3session.dtd
@@ -10,7 +10,7 @@
 <!ATTLIST prover memlimit CDATA #IMPLIED>
 <!ATTLIST prover steplimit CDATA #IMPLIED>
 
-<!ELEMENT file (path*) (theory*)>
+<!ELEMENT file (path*, theory*)>
 <!ATTLIST file name CDATA #IMPLIED>
 <!ATTLIST file verified CDATA #IMPLIED>
 <!ATTLIST file proved CDATA #IMPLIED>