diff --git a/biblio-tools/v1/crossref/prefixes/expand.ini b/biblio-tools/v1/crossref/prefixes/expand.ini
index 4888bae..28b13d5 100644
--- a/biblio-tools/v1/crossref/prefixes/expand.ini
+++ b/biblio-tools/v1/crossref/prefixes/expand.ini
@@ -38,23 +38,39 @@
 path = value
 value = get('value').split('/').filter(i => i.match(/^10./)).pop()
 
-[expand/assign]
+# On crée une URL uniqument avec les prefixes non vides
+[expand/swing]
+test = get('value').isEmpty()
+reverse = true
+
+[expand/swing/assign]
 path = url
 value = fix('https://api.crossref.org/prefixes', self.value).join('/')
 
-[expand/URLFetch]
+[expand/swing/URLFetch]
 target = result
 url = get('url')
 json = true
 timeout = 60000
-noerror = false
+noerror = true
+retries = 1
 
-[expand/replace]
+[expand/swing/replace]
 path = id
 value = get('id')
 
 path = value
 value = get('result.message.name', 'n/a')
 
+[expand/transit]
+
+# On marque les prefixes vides (qui n'ont pas été traité par le swing précédent)
+[expand/swing]
+test = get('value').isEmpty()
+
+[expand/swing/assign]
+path = value
+value = fix('n/a')
+
 [dump]
 indent = env('indent', false)