diff --git a/poincare/src/parsing/parser.cpp b/poincare/src/parsing/parser.cpp
index b45e22af7..ac81e1b14 100644
--- a/poincare/src/parsing/parser.cpp
+++ b/poincare/src/parsing/parser.cpp
@@ -361,6 +361,10 @@ void Parser::parseCustomIdentifier(Expression & leftHandSide, const char * name,
     return;
   }
   Expression parameter = parseCommaSeparatedList();
+  if (m_status != Status::Progress) {
+    return;
+  }
+  assert(!parameter.isUninitialized());
   if (parameter.numberOfChildren() != 1) {
     m_status = Status::Error; // Unexpected number of paramters.
     return;