diff --git a/.gitignore b/.gitignore
index e8faaf926..89f277b5d 100644
--- a/.gitignore
+++ b/.gitignore
@@ -100,3 +100,4 @@ target
 *.gobrafied
 *.internal
 .devcontainer
+.metals
diff --git a/router/dataplane_spec.gobra b/router/dataplane_spec.gobra
index 10941b4fe..e24e07d75 100644
--- a/router/dataplane_spec.gobra
+++ b/router/dataplane_spec.gobra
@@ -149,7 +149,7 @@ pred hideLocalIA(p *addr.IA) {
 }
 
 pred (err scmpError) ErrorMem() {
-	err.Cause != nil && err.Cause.ErrorMem()
+	err.Cause != nil ==> err.Cause.ErrorMem()
 }
 
 scmpError implements error