diff --git a/dumux/common/parameters.hh b/dumux/common/parameters.hh
index 6d7778d48125caa47a8de6f437acacc5a11a4395..515be93cdbe15ee342181903a97aea198adca60f 100644
--- a/dumux/common/parameters.hh
+++ b/dumux/common/parameters.hh
@@ -382,7 +382,7 @@ private:
         }
 
         // retrieve actual parameter from the parameter tree
-        if (Params::tree().hasKey(finalName)) {
+        if (!Params::tree().hasKey(finalName)) {
             DUNE_THROW(Dune::InvalidStateException,
                        "Mandatory parameter '" << finalName
                        << "' was not specified.");