1 files changed, 1 insertions, 1 deletions

diff --git a/subprojects/language/src/main/java/tools/refinery/language/Problem.xtext b/subprojects/language/src/main/java/tools/refinery/language/Problem.xtext
index 74b0d50e..f7b86dca 100644
--- a/subprojects/language/src/main/java/tools/refinery/language/Problem.xtext
+++ b/subprojects/language/src/main/java/tools/refinery/language/Problem.xtext
@@ -49,7 +49,7 @@ RuleDefinition:
         ".";
 
 Parameter:
-        parameterType=[Relation|QualifiedName]? name=Identifier;
+        (modality=Modality? parameterType=[Relation|QualifiedName])? name=Identifier;
 
 Conjunction:
         literals+=Literal ("," literals+=Literal)*;