diff --git a/libsolidity/codegen/MultiUseYulFunctionCollector.cpp b/libsolidity/codegen/MultiUseYulFunctionCollector.cpp
index 0049deb78..541171818 100644
--- a/libsolidity/codegen/MultiUseYulFunctionCollector.cpp
+++ b/libsolidity/codegen/MultiUseYulFunctionCollector.cpp
@@ -33,8 +33,11 @@ string MultiUseYulFunctionCollector::requestedFunctions()
 {
 	string result;
 	for (auto const& f: m_requestedFunctions)
+	{
+		solAssert(f.second != "<<STUB<<", "");
 		// std::map guarantees ascending order when iterating through its keys.
 		result += f.second;
+	}
 	m_requestedFunctions.clear();
 	return result;
 }
@@ -43,9 +46,10 @@ string MultiUseYulFunctionCollector::createFunction(string const& _name, functio
 {
 	if (!m_requestedFunctions.count(_name))
 	{
+		m_requestedFunctions[_name] = "<<STUB<<";
 		string fun = _creator();
 		solAssert(!fun.empty(), "");
-		solAssert(fun.find("function " + _name) != string::npos, "Function not properly named.");
+		solAssert(fun.find("function " + _name + "(") != string::npos, "Function not properly named.");
 		m_requestedFunctions[_name] = std::move(fun);
 	}
 	return _name;