diff --git a/libsolidity/codegen/ExpressionCompiler.cpp b/libsolidity/codegen/ExpressionCompiler.cpp
index 42756a8de..490ec3d1b 100644
--- a/libsolidity/codegen/ExpressionCompiler.cpp
+++ b/libsolidity/codegen/ExpressionCompiler.cpp
@@ -413,7 +413,10 @@ bool ExpressionCompiler::visit(UnaryOperation const& _unaryOperation)
 
 	if (FunctionDefinition const* function = _unaryOperation.annotation().userDefinedFunction)
 	{
-		solAssert(function->isFree(), "Only free functions can be bound to a user type operator.");
+		solAssert(
+			function->isFree() || function->libraryFunction(),
+			"Only file-level functions and library functions can be bound to a user type operator."
+		);
 
 		FunctionType const* functionType = dynamic_cast<FunctionType const*>(
 			function->libraryFunction() ? function->typeViaContractName() : function->type()
@@ -537,7 +540,10 @@ bool ExpressionCompiler::visit(BinaryOperation const& _binaryOperation)
 	Expression const& rightExpression = _binaryOperation.rightExpression();
 	if (FunctionDefinition const* function =_binaryOperation.annotation().userDefinedFunction)
 	{
-		solAssert(function->isFree(), "Only free function can be bound to a user type operator.");
+		solAssert(
+			function->isFree() || function->libraryFunction(),
+			"Only file-level functions and library functions can be bound to a user type operator."
+		);
 		FunctionType const* functionType = dynamic_cast<FunctionType const*>(
 			function->libraryFunction() ? function->typeViaContractName() : function->type()
 		);
diff --git a/libsolidity/codegen/ir/IRGeneratorForStatements.cpp b/libsolidity/codegen/ir/IRGeneratorForStatements.cpp
index 5beddf3a3..70b3aaf59 100644
--- a/libsolidity/codegen/ir/IRGeneratorForStatements.cpp
+++ b/libsolidity/codegen/ir/IRGeneratorForStatements.cpp
@@ -679,7 +679,7 @@ bool IRGeneratorForStatements::visit(UnaryOperation const& _unaryOperation)
 		setLocation(_unaryOperation);
 
 		solAssert(
-			dynamic_cast<SourceUnit const*>(function->scope()),
+			function->isFree() || function->libraryFunction(),
 			"Only file-level functions and library functions can be bound to a user type operator."
 		);
 
@@ -824,7 +824,7 @@ bool IRGeneratorForStatements::visit(BinaryOperation const& _binOp)
 		setLocation(_binOp);
 
 		solAssert(
-			dynamic_cast<SourceUnit const*>(function->scope()),
+			function->isFree() || function->libraryFunction(),
 			"Only file-level functions and library functions can be bound to a user type operator."
 		);
 
diff --git a/test/libsolidity/semanticTests/operators/custom/operator_bound_to_library_function.sol b/test/libsolidity/semanticTests/operators/custom/operator_bound_to_library_function.sol
new file mode 100644
index 000000000..c36fe2ed3
--- /dev/null
+++ b/test/libsolidity/semanticTests/operators/custom/operator_bound_to_library_function.sol
@@ -0,0 +1,33 @@
+==== Source: a.sol ====
+library L {
+    type Int is int128;
+
+    function add(Int, Int) pure public returns (Int) {
+        return Int.wrap(7);
+    }
+
+    function sub(Int) pure public returns (Int) {
+        return Int.wrap(5);
+    }
+}
+==== Source: b.sol ====
+import "a.sol" as a;
+
+contract C {
+    using {a.L.add as +} for a.L.Int;
+    using {a.L.sub as -} for a.L.Int;
+
+    function f() pure public returns (a.L.Int) {
+	return a.L.Int.wrap(0) + a.L.Int.wrap(0);
+    }
+
+    function g() pure public returns (a.L.Int) {
+	return - a.L.Int.wrap(0);
+    }
+}
+
+// ====
+// compileViaYul: also
+// ----
+// f() -> 7
+// g() -> 5