diff --git a/libsolidity/analysis/TypeChecker.cpp b/libsolidity/analysis/TypeChecker.cpp
index 25bd4a915197..36f26e49d5d7 100644
--- a/libsolidity/analysis/TypeChecker.cpp
+++ b/libsolidity/analysis/TypeChecker.cpp
@@ -1632,10 +1632,13 @@ bool TypeChecker::visit(UnaryOperation const& _operation)
 		resultType = builtinResult;
 	else if (!matchingDefinitions.empty())
 	{
-		// This is checked along with `using for` directive but the error is not fatal.
-		if (matchingDefinitions.size() != 1)
-			solAssert(m_errorReporter.hasErrors());
-
+		// Duplicate user-defined operator bindings are flagged later by
+		// endVisit(UsingForDirective) (error 4705). When a function body that
+		// uses the operator is type-checked before the directive is fully
+		// processed (e.g. for self-referential `using for` definitions), no
+		// error has been emitted yet and the previous solAssert(hasErrors())
+		// triggered an ICE. Pick the first match and let the directive's own
+		// duplicate check surface the error.
 		operatorDefinition = *matchingDefinitions.begin();
 	}
 	else
@@ -1697,10 +1700,13 @@ void TypeChecker::endVisit(BinaryOperation const& _operation)
 		commonType = builtinResult.get();
 	else if (!matchingDefinitions.empty())
 	{
-		// This is checked along with `using for` directive but the error is not fatal.
-		if (matchingDefinitions.size() != 1)
-			solAssert(m_errorReporter.hasErrors());
-
+		// Duplicate user-defined operator bindings are flagged later by
+		// endVisit(UsingForDirective) (error 4705). When a function body that
+		// uses the operator is type-checked before the directive is fully
+		// processed (e.g. for self-referential `using for` definitions), no
+		// error has been emitted yet and the previous solAssert(hasErrors())
+		// triggered an ICE. Pick the first match and let the directive's own
+		// duplicate check surface the error.
 		operatorDefinition = *matchingDefinitions.begin();
 
 		// Set common type to the type used in the `using for` directive.
diff --git a/test/libsolidity/syntaxTests/operators/userDefined/duplicate_binary_operator_self_referential.sol b/test/libsolidity/syntaxTests/operators/userDefined/duplicate_binary_operator_self_referential.sol
new file mode 100644
index 000000000000..c9b71266f712
--- /dev/null
+++ b/test/libsolidity/syntaxTests/operators/userDefined/duplicate_binary_operator_self_referential.sol
@@ -0,0 +1,11 @@
+// Used to cause ICE in TypeChecker::endVisit(BinaryOperation) when a
+// function body referenced an operator that had multiple matching
+// `using for` definitions before the directive's own duplicate check
+// (error 4705) had a chance to run.
+type T is int256;
+function sub(T a, T b) pure returns (T) {}
+function add(T a, T b) pure returns (T) { T c = a + b; c; }
+using {sub as +, add as +} for T global;
+// ----
+// TypeError 4705: (267-270): User-defined binary operator + has more than one definition matching the operand type visible in the current scope.
+// TypeError 4705: (277-280): User-defined binary operator + has more than one definition matching the operand type visible in the current scope.
diff --git a/test/libsolidity/syntaxTests/operators/userDefined/duplicate_unary_operator_self_referential.sol b/test/libsolidity/syntaxTests/operators/userDefined/duplicate_unary_operator_self_referential.sol
new file mode 100644
index 000000000000..536d50b15542
--- /dev/null
+++ b/test/libsolidity/syntaxTests/operators/userDefined/duplicate_unary_operator_self_referential.sol
@@ -0,0 +1,11 @@
+// Used to cause ICE in TypeChecker::visit(UnaryOperation) when a function
+// body referenced an operator that had multiple matching `using for`
+// definitions before the directive's own duplicate check (error 4705)
+// had a chance to run.
+type T is int256;
+function neg1(T a) pure returns (T) { return -a; }
+function neg2(T a) pure returns (T) { return a; }
+using {neg1 as -, neg2 as -} for T global;
+// ----
+// TypeError 4705: (262-266): User-defined unary operator - has more than one definition matching the operand type visible in the current scope.
+// TypeError 4705: (273-277): User-defined unary operator - has more than one definition matching the operand type visible in the current scope.