diff --git a/src/rougail/annotator.py b/src/rougail/annotator.py
index 48b7cd60..9a178ed7 100644
--- a/src/rougail/annotator.py
+++ b/src/rougail/annotator.py
@@ -1037,6 +1037,9 @@ class ConstraintAnnotator:
                         raise DictConsistencyError(_(f"All '{param.type}' variables must have a value in order to calculate {fill.target}"))
                     if param.type == 'suffix' and hasattr(param, 'text'):
                         raise DictConsistencyError(_(f"All '{param.type}' variables must not have a value in order to calculate {fill.target}"))
+                    if param.type == 'string':
+                        if not hasattr(param, 'text'):
+                            param.text = None
                     if param.type == 'variable':
                         try:
                             param.text, suffix = self.objectspace.paths.get_variable_path(param.text,
diff --git a/tests/dictionaries/51redefine_remove_check/00-base.xml b/tests/dictionaries/51redefine_remove_check/00-base.xml
index 4de0c2c9..0fbbb510 100644
--- a/tests/dictionaries/51redefine_remove_check/00-base.xml
+++ b/tests/dictionaries/51redefine_remove_check/00-base.xml
@@ -12,7 +12,9 @@
 
     <constraints>
         <check name="valid_enum" target="mode_conteneur_actif">
-            <param>['a','b','c']</param>
+            <param>a</param>
+            <param>b</param>
+            <param>c</param>
         </check>
     </constraints>
 
diff --git a/tests/dictionaries/88valid_enum_not_number/00-base.xml b/tests/dictionaries/88valid_enum_not_number/00-base.xml
index 67db377c..f6d92700 100644
--- a/tests/dictionaries/88valid_enum_not_number/00-base.xml
+++ b/tests/dictionaries/88valid_enum_not_number/00-base.xml
@@ -17,7 +17,9 @@
 
     <constraints>
         <check name="valid_enum" target="enumvar">
-            <param>['a', 'b', 'c']</param>
+            <param>a</param>
+            <param>b</param>
+            <param>c</param>
         </check>
     </constraints>
 
diff --git a/tests/dictionaries/88valid_enum_numberdefaultstring/00-base.xml b/tests/dictionaries/88valid_enum_numberdefaultstring/00-base.xml
index 92f61c26..fda4ef95 100644
--- a/tests/dictionaries/88valid_enum_numberdefaultstring/00-base.xml
+++ b/tests/dictionaries/88valid_enum_numberdefaultstring/00-base.xml
@@ -19,7 +19,9 @@
 
     <constraints>
         <check name="valid_enum" target="enumvar">
-            <param>[1, 2, 3]</param>
+            <param>1</param>
+            <param>2</param>
+            <param>3</param>
         </check>
     </constraints>