diff --git a/biblio-tools/v1/hal/works/expand.ini b/biblio-tools/v1/hal/works/expand.ini
index 8867278..d3248ec 100644
--- a/biblio-tools/v1/hal/works/expand.ini
+++ b/biblio-tools/v1/hal/works/expand.ini
@@ -85,7 +85,7 @@
 value = get('text/body/listBibl/biblFull/sourceDesc/biblStruct/idno/$t')
 
 path = value
-value = self() 
+value = self()
 
 [map/spawn/replace]
 path = id
@@ -94,7 +94,6 @@
 path = value
 value = get('value')
 
-
 # Croisements des resultats et des dois
 [exchange]
 value = get('input').map((i) => ({ ...i, value:_.get(_.find(self.output, {id:i.value}), 'value') }))
@@ -111,5 +110,19 @@
 path = value
 value = fix('n/a')
 
+# Prevents keys from containing the $ character (which is forbidden by nodejs mongoDB driver)
+[OBJFlatten]
+separator = fix('/')
+safe = false
+
+[exchange]
+value = self().mapKeys((value, key) => key.replace(/\$/g, '_'))
+
+[OBJFlatten]
+separator = fix('/')
+reverse = true
+safe = false
+# ...
+
 [dump]
 indent = env('indent', false)