diff --git a/libsolidity/analysis/ControlFlowBuilder.cpp b/libsolidity/analysis/ControlFlowBuilder.cpp
index d660318ed..0c4bcfef3 100644
--- a/libsolidity/analysis/ControlFlowBuilder.cpp
+++ b/libsolidity/analysis/ControlFlowBuilder.cpp
@@ -65,7 +65,7 @@ bool ControlFlowBuilder::visit(BinaryOperation const& _operation)
 		case Token::And:
 		{
 			visitNode(_operation);
-			solAssert(!_operation.annotation().userDefinedFunction);
+			solAssert(!_operation.annotation().userDefinedFunction.set());
 			appendControlFlow(_operation.leftExpression());
 
 			auto nodes = splitFlow<2>();
@@ -75,13 +75,13 @@ bool ControlFlowBuilder::visit(BinaryOperation const& _operation)
 		}
 		default:
 		{
-			if (_operation.annotation().userDefinedFunction)
+			if (_operation.annotation().userDefinedFunction.set())
 			{
 				visitNode(_operation);
 				_operation.leftExpression().accept(*this);
 				_operation.rightExpression().accept(*this);
 
-				m_currentNode->functionDefinition = _operation.annotation().userDefinedFunction;
+				m_currentNode->functionDefinition = *_operation.annotation().userDefinedFunction;
 
 				auto nextNode = newLabel();
 
@@ -99,10 +99,10 @@ bool ControlFlowBuilder::visit(UnaryOperation const& _operation)
 {
 	solAssert(!!m_currentNode);
 
-	if (_operation.annotation().userDefinedFunction)
+	if (_operation.annotation().userDefinedFunction.set())
 	{
 		visitNode(_operation);
-		m_currentNode->functionDefinition = _operation.annotation().userDefinedFunction;
+		m_currentNode->functionDefinition = *_operation.annotation().userDefinedFunction;
 
 		auto nextNode = newLabel();
 
diff --git a/libsolidity/analysis/FunctionCallGraph.cpp b/libsolidity/analysis/FunctionCallGraph.cpp
index 8f7a816d3..502bd0221 100644
--- a/libsolidity/analysis/FunctionCallGraph.cpp
+++ b/libsolidity/analysis/FunctionCallGraph.cpp
@@ -206,15 +206,15 @@ bool FunctionCallGraphBuilder::visit(MemberAccess const& _memberAccess)
 
 bool FunctionCallGraphBuilder::visit(BinaryOperation const& _binaryOperation)
 {
-	if (FunctionDefinition const* function = _binaryOperation.annotation().userDefinedFunction)
-		functionReferenced(*function, true /* called directly */);
+	if (_binaryOperation.annotation().userDefinedFunction.set())
+		functionReferenced(**_binaryOperation.annotation().userDefinedFunction, true /* called directly */);
 	return true;
 }
 
 bool FunctionCallGraphBuilder::visit(UnaryOperation const& _unaryOperation)
 {
-	if (FunctionDefinition const* function = _unaryOperation.annotation().userDefinedFunction)
-		functionReferenced(*function, true /* called directly */);
+	if (_unaryOperation.annotation().userDefinedFunction.set())
+		functionReferenced(**_unaryOperation.annotation().userDefinedFunction, true /* called directly */);
 	return true;
 }
 
diff --git a/libsolidity/analysis/TypeChecker.cpp b/libsolidity/analysis/TypeChecker.cpp
index 15c4ef1eb..cac55ceed 100644
--- a/libsolidity/analysis/TypeChecker.cpp
+++ b/libsolidity/analysis/TypeChecker.cpp
@@ -1736,7 +1736,8 @@ bool TypeChecker::visit(UnaryOperation const& _operation)
 		*currentDefinitionScope(),
 		true // _unaryOperation
 	);
-	_operation.annotation().userDefinedFunction = userDefinedOperatorResult;
+	if (userDefinedOperatorResult)
+		_operation.annotation().userDefinedFunction = userDefinedOperatorResult;
 	FunctionType const* userDefinedFunctionType = nullptr;
 	if (userDefinedOperatorResult)
 		userDefinedFunctionType = &dynamic_cast<FunctionType const&>(
@@ -1792,7 +1793,8 @@ void TypeChecker::endVisit(BinaryOperation const& _operation)
 		*currentDefinitionScope(),
 		false // _unaryOperation
 	);
-	_operation.annotation().userDefinedFunction = userDefinedOperatorResult;
+	if (userDefinedOperatorResult)
+		_operation.annotation().userDefinedFunction = userDefinedOperatorResult;
 	FunctionType const* userDefinedFunctionType = nullptr;
 	if (userDefinedOperatorResult)
 		userDefinedFunctionType = &dynamic_cast<FunctionType const&>(
diff --git a/libsolidity/analysis/ViewPureChecker.cpp b/libsolidity/analysis/ViewPureChecker.cpp
index a7f18f298..c73983c29 100644
--- a/libsolidity/analysis/ViewPureChecker.cpp
+++ b/libsolidity/analysis/ViewPureChecker.cpp
@@ -333,14 +333,20 @@ void ViewPureChecker::reportFunctionCallMutability(StateMutability _mutability,
 
 void ViewPureChecker::endVisit(BinaryOperation const& _binaryOperation)
 {
-	if (_binaryOperation.annotation().userDefinedFunction)
-		reportFunctionCallMutability(_binaryOperation.annotation().userDefinedFunction->stateMutability(), _binaryOperation.location());
+	if (_binaryOperation.annotation().userDefinedFunction.set())
+	{
+		solAssert(*_binaryOperation.annotation().userDefinedFunction);
+		reportFunctionCallMutability((*_binaryOperation.annotation().userDefinedFunction)->stateMutability(), _binaryOperation.location());
+	}
 }
 
 void ViewPureChecker::endVisit(UnaryOperation const& _unaryOperation)
 {
-	if (_unaryOperation.annotation().userDefinedFunction)
-		reportFunctionCallMutability(_unaryOperation.annotation().userDefinedFunction->stateMutability(), _unaryOperation.location());
+	if (_unaryOperation.annotation().userDefinedFunction.set())
+	{
+		solAssert((*_unaryOperation.annotation().userDefinedFunction));
+		reportFunctionCallMutability((*_unaryOperation.annotation().userDefinedFunction)->stateMutability(), _unaryOperation.location());
+	}
 }
 
 void ViewPureChecker::endVisit(FunctionCall const& _functionCall)
diff --git a/libsolidity/ast/ASTAnnotations.h b/libsolidity/ast/ASTAnnotations.h
index a9f7abd21..b85eb3ad0 100644
--- a/libsolidity/ast/ASTAnnotations.h
+++ b/libsolidity/ast/ASTAnnotations.h
@@ -314,7 +314,7 @@ struct MemberAccessAnnotation: ExpressionAnnotation
 
 struct OperationAnnotation: ExpressionAnnotation
 {
-	FunctionDefinition const* userDefinedFunction = nullptr;
+	util::SetOnce<FunctionDefinition const*> userDefinedFunction;
 };
 
 struct BinaryOperationAnnotation: OperationAnnotation
diff --git a/libsolidity/ast/ASTJsonExporter.cpp b/libsolidity/ast/ASTJsonExporter.cpp
index 5e86cc70e..23aa0903f 100644
--- a/libsolidity/ast/ASTJsonExporter.cpp
+++ b/libsolidity/ast/ASTJsonExporter.cpp
@@ -833,8 +833,8 @@ bool ASTJsonExporter::visit(UnaryOperation const& _node)
 		make_pair("operator", TokenTraits::toString(_node.getOperator())),
 		make_pair("subExpression", toJson(_node.subExpression()))
 	};
-	if (FunctionDefinition const* referencedDeclaration = _node.annotation().userDefinedFunction)
-		attributes.emplace_back("function", nodeId(*referencedDeclaration));
+	if (_node.annotation().userDefinedFunction.set())
+		attributes.emplace_back("function", nodeId(**_node.annotation().userDefinedFunction));
 	appendExpressionAttributes(attributes, _node.annotation());
 	setJsonNode(_node, "UnaryOperation", std::move(attributes));
 	return false;
@@ -848,8 +848,8 @@ bool ASTJsonExporter::visit(BinaryOperation const& _node)
 		make_pair("rightExpression", toJson(_node.rightExpression())),
 		make_pair("commonType", typePointerToJson(_node.annotation().commonType)),
 	};
-	if (FunctionDefinition const* function = _node.annotation().userDefinedFunction)
-		attributes.emplace_back("function", nodeId(*function));
+	if (_node.annotation().userDefinedFunction.set())
+		attributes.emplace_back("function", nodeId(**_node.annotation().userDefinedFunction));
 	appendExpressionAttributes(attributes, _node.annotation());
 	setJsonNode(_node, "BinaryOperation", std::move(attributes));
 	return false;
diff --git a/libsolidity/codegen/ExpressionCompiler.cpp b/libsolidity/codegen/ExpressionCompiler.cpp
index f1fe2cac7..e703f1cfc 100644
--- a/libsolidity/codegen/ExpressionCompiler.cpp
+++ b/libsolidity/codegen/ExpressionCompiler.cpp
@@ -411,8 +411,10 @@ bool ExpressionCompiler::visit(UnaryOperation const& _unaryOperation)
 {
 	CompilerContext::LocationSetter locationSetter(m_context, _unaryOperation);
 
-	if (FunctionDefinition const* function = _unaryOperation.annotation().userDefinedFunction)
+	if (_unaryOperation.annotation().userDefinedFunction.set())
 	{
+		FunctionDefinition const* function = *_unaryOperation.annotation().userDefinedFunction;
+		solAssert(function);
 		solAssert(
 			function->isFree() || function->libraryFunction(),
 			"Only file-level functions and library functions can be bound to a user type operator."
@@ -538,8 +540,10 @@ bool ExpressionCompiler::visit(BinaryOperation const& _binaryOperation)
 	CompilerContext::LocationSetter locationSetter(m_context, _binaryOperation);
 	Expression const& leftExpression = _binaryOperation.leftExpression();
 	Expression const& rightExpression = _binaryOperation.rightExpression();
-	if (FunctionDefinition const* function =_binaryOperation.annotation().userDefinedFunction)
+	if (_binaryOperation.annotation().userDefinedFunction.set())
 	{
+		FunctionDefinition const* function = *_binaryOperation.annotation().userDefinedFunction;
+		solAssert(function);
 		solAssert(
 			function->isFree() || function->libraryFunction(),
 			"Only file-level functions and library functions can be bound to a user type operator."
diff --git a/libsolidity/codegen/ir/IRGeneratorForStatements.cpp b/libsolidity/codegen/ir/IRGeneratorForStatements.cpp
index 94673959c..963b059d7 100644
--- a/libsolidity/codegen/ir/IRGeneratorForStatements.cpp
+++ b/libsolidity/codegen/ir/IRGeneratorForStatements.cpp
@@ -673,11 +673,13 @@ bool IRGeneratorForStatements::visit(UnaryOperation const& _unaryOperation)
 {
 	setLocation(_unaryOperation);
 
-	if (FunctionDefinition const* function = _unaryOperation.annotation().userDefinedFunction)
+	if (_unaryOperation.annotation().userDefinedFunction.set())
 	{
 		_unaryOperation.subExpression().accept(*this);
 		setLocation(_unaryOperation);
 
+		FunctionDefinition const* function = *_unaryOperation.annotation().userDefinedFunction;
+		solAssert(function);
 		solAssert(
 			function->isFree() || function->libraryFunction(),
 			"Only file-level functions and library functions can be bound to a user type operator."
@@ -817,12 +819,14 @@ bool IRGeneratorForStatements::visit(BinaryOperation const& _binOp)
 {
 	setLocation(_binOp);
 
-	if (FunctionDefinition const* function = _binOp.annotation().userDefinedFunction)
+	if (_binOp.annotation().userDefinedFunction.set())
 	{
 		_binOp.leftExpression().accept(*this);
 		_binOp.rightExpression().accept(*this);
 		setLocation(_binOp);
 
+		FunctionDefinition const* function = *_binOp.annotation().userDefinedFunction;
+		solAssert(function);
 		solAssert(
 			function->isFree() || function->libraryFunction(),
 			"Only file-level functions and library functions can be bound to a user type operator."