diff --git a/codyze-specification-languages/coko/coko-dsl/src/main/kotlin/de/fraunhofer/aisec/codyze/specificationLanguages/coko/dsl/host/SpecEvaluator.kt b/codyze-specification-languages/coko/coko-dsl/src/main/kotlin/de/fraunhofer/aisec/codyze/specificationLanguages/coko/dsl/host/SpecEvaluator.kt
index 5b2be8523..48553d8b5 100644
--- a/codyze-specification-languages/coko/coko-dsl/src/main/kotlin/de/fraunhofer/aisec/codyze/specificationLanguages/coko/dsl/host/SpecEvaluator.kt
+++ b/codyze-specification-languages/coko/coko-dsl/src/main/kotlin/de/fraunhofer/aisec/codyze/specificationLanguages/coko/dsl/host/SpecEvaluator.kt
@@ -73,7 +73,7 @@ class SpecEvaluator {
                     // TODO: check for all implementations!
                     implementationsAndInstances
                         .filter { (it, _) -> it.createType().isSubtypeOf(param.type) }
-                        .mapNotNull { (it, _) ->
+                        .map { (it, paramInstance) ->
                             val primaryConstructor =
                                 checkNotNull(it.primaryConstructor) {
                                     "Could not create an instance of ${it.qualifiedName} to pass to rule " +
@@ -88,13 +88,13 @@ class SpecEvaluator {
                                 "Could not create an instance of ${it.qualifiedName} to pass to rule " +
                                     "\"${rule.name}\" because it's primary constructor expects arguments. Aborting."
                             }
+                            // TODO: how do we access primaryConstructor.arity ? -> then we would
+                            // not need the try..catch
                             try {
-                                primaryConstructor.call()
+                                primaryConstructor.call(paramInstance)
                             } catch (e: IllegalArgumentException) {
-                                logger.debug {
-                                    "Calling constructor '$primaryConstructor' without arguments failed ($e)"
-                                }
-                                null
+                                logger.debug { "Called constructor '$primaryConstructor' without paramInstance ($e)" }
+                                primaryConstructor.call()
                             }
                         }[0]
                 }