diff --git a/modules/patterns/bbch.plan b/modules/patterns/bbch.plan
index 5a34b5aa7d26e5b49f56fada5a6ebdf47f2f3ebf..5d4014da7e5a4a30e95cee1a6abeb373cdb07ffb 100644
--- a/modules/patterns/bbch.plan
+++ b/modules/patterns/bbch.plan
@@ -41,10 +41,10 @@
     <pattern>
       [ @form =^ "BBCH" ]
       [ @form == "-"]?
-      (number:[ @form =~ "[0-9]{2}$" ])
+      (number:[ @form =~ "\\d{2}$" ])
     </pattern>
     <actions>
-      <createAnnotation layer="bbch" features='canonical-form=("BBCH " ^ group:number),uri=("http://ontology.inrae.fr/ppdo/ontology/bbch_globalScale_secondaryStage_BBCH" ^ group:number)'/>
+      <createAnnotation layer="bbch" features='canonical-form=("BBCH " ^ (group:number =~ "..$")),uri=("http://ontology.inrae.fr/ppdo/ontology/bbch_globalScale_secondaryStage_BBCH" ^ (group:number =~ "..$"))'/>
     </actions>
     <constantAnnotationFeatures>type=BBCH-DD</constantAnnotationFeatures>
   </BBCH_DD>