diff --git a/patcher/operator_override.go b/patcher/operator_override.go
index 96e6894c..428454f5 100644
--- a/patcher/operator_override.go
+++ b/patcher/operator_override.go
@@ -131,11 +131,11 @@ func checkType(fnType conf.Tag, fn string, operator string) {
 
 func checkFunc(fn *builtin.Function, name string, operator string) {
 	if len(fn.Types) == 0 {
-		panic(fmt.Errorf("function %s for %s operator misses types", name, operator))
+		panic(fmt.Errorf("function %q for %q operator misses types", name, operator))
 	}
 	for _, t := range fn.Types {
 		if t.NumIn() != 2 || t.NumOut() != 1 {
-			panic(fmt.Errorf("function %s for %s operator does not have a correct signature", name, operator))
+			panic(fmt.Errorf("function %q for %q operator does not have a correct signature", name, operator))
 		}
 	}
 }
diff --git a/test/operator/operator_test.go b/test/operator/operator_test.go
index 99817eff..a19c191d 100644
--- a/test/operator/operator_test.go
+++ b/test/operator/operator_test.go
@@ -5,6 +5,7 @@ import (
 	"testing"
 	"time"
 
+	"github.com/stretchr/testify/assert"
 	"github.com/stretchr/testify/require"
 
 	"github.com/expr-lang/expr"
@@ -108,7 +109,7 @@ func TestOperator_Function_WithTypes(t *testing.T) {
 		"bar": Value{2},
 	}
 
-	require.PanicsWithError(t, `function Add for + operator misses types`, func() {
+	assert.PanicsWithError(t, `function "Add" for "+" operator misses types`, func() {
 		_, _ = expr.Compile(
 			`foo + bar`,
 			expr.Env(env),
@@ -119,7 +120,7 @@ func TestOperator_Function_WithTypes(t *testing.T) {
 		)
 	})
 
-	require.PanicsWithError(t, `function Add for + operator does not have a correct signature`, func() {
+	assert.PanicsWithError(t, `function "Add" for "+" operator does not have a correct signature`, func() {
 		_, _ = expr.Compile(
 			`foo + bar`,
 			expr.Env(env),
@@ -131,7 +132,6 @@ func TestOperator_Function_WithTypes(t *testing.T) {
 			),
 		)
 	})
-
 }
 
 func TestOperator_FunctionOverTypesPrecedence(t *testing.T) {