diff --git a/ChangeLog.md b/ChangeLog.md
--- a/ChangeLog.md
+++ b/ChangeLog.md
@@ -1,3 +1,8 @@
+# 6.3.0.1
+
+  - Fix MacOS X compilation.
+
+
 # 6.3.0.0
 
   - Update to Bibutils 6.3.
diff --git a/bibutils/xml.h b/bibutils/xml.h
--- a/bibutils/xml.h
+++ b/bibutils/xml.h
@@ -37,7 +37,7 @@
 int    xml_has_attribute        ( xml *node, const char *attribute, const char *attribute_value );
 char * xml_parse                ( char *p, xml *onode );
 
-char * xml_pns; /* global Namespace */
+extern char *   xml_pns; /* global Namespace */
 
 #endif
 
diff --git a/hs-bibutils.cabal b/hs-bibutils.cabal
--- a/hs-bibutils.cabal
+++ b/hs-bibutils.cabal
@@ -1,5 +1,5 @@
 name:               hs-bibutils
-version:            6.3.0.0
+version:            6.3.0.1
 homepage:           https://github.com/wilx/hs-bibutils
 
 synopsis:           Haskell bindings to bibutils, the bibliography