diff --git a/config/types.go b/config/types.go
index baa073ab460e..fccae22b5ae0 100644
--- a/config/types.go
+++ b/config/types.go
@@ -360,7 +360,7 @@ func (p OptionalString) String() string {
 	if p.value == nil {
 		return "default"
 	}
-	return fmt.Sprintf("%d", p.value)
+	return *p.value
 }
 
 var _ json.Unmarshaler = (*OptionalInteger)(nil)
diff --git a/config/types_test.go b/config/types_test.go
index 2477f8bcf9a2..3a1fd6a8426a 100644
--- a/config/types_test.go
+++ b/config/types_test.go
@@ -407,11 +407,13 @@ func TestOptionalString(t *testing.T) {
 		t.Fatal("should be the default")
 	}
 	if val := defaultOptionalString.WithDefault(""); val != "" {
-		t.Errorf("optional integer should have been empty, got %s", val)
+		t.Errorf("optional string should have been empty, got %s", val)
+	}
+	if val := defaultOptionalString.String(); val != "default" {
+		t.Fatalf("default optional string should be the 'default' string, got %s", val)
 	}
-
 	if val := defaultOptionalString.WithDefault("foo"); val != "foo" {
-		t.Errorf("optional integer should have been foo, got %s", val)
+		t.Errorf("optional string should have been foo, got %s", val)
 	}
 
 	var filledStr OptionalString
@@ -420,17 +422,20 @@ func TestOptionalString(t *testing.T) {
 		t.Fatal("should not be the default")
 	}
 	if val := filledStr.WithDefault("bar"); val != "foo" {
-		t.Errorf("optional integer should have been foo, got %s", val)
+		t.Errorf("optional string should have been foo, got %s", val)
+	}
+	if val := filledStr.String(); val != "foo" {
+		t.Fatalf("optional string should have been foo, got %s", val)
 	}
-
 	filledStr = OptionalString{value: makeStringPointer("")}
 	if val := filledStr.WithDefault("foo"); val != "" {
-		t.Errorf("optional integer should have been 0, got %s", val)
+		t.Errorf("optional string should have been 0, got %s", val)
 	}
 
 	for jsonStr, goValue := range map[string]OptionalString{
 		"null":     {},
 		"\"0\"":    {value: makeStringPointer("0")},
+		"\"\"":     {value: makeStringPointer("")},
 		`"1"`:      {value: makeStringPointer("1")},
 		`"-1"`:     {value: makeStringPointer("-1")},
 		`"qwerty"`: {value: makeStringPointer("qwerty")},