diff --git a/README.md b/README.md
index 4d12a82..eb53852 100644
--- a/README.md
+++ b/README.md
@@ -175,7 +175,7 @@ use log::Level;
 struct CustomLog {}
 
 impl LogAppender for CustomLog {
-    fn do_logs(&self, records: &[FastLogRecord]) {
+    fn do_logs(&mut self, records: &[FastLogRecord]) {
         for record in records {
             let now = DateTime::from(record.now);
             let data;
diff --git a/example/src/custom_appender.rs b/example/src/custom_appender.rs
index 7e19c1c..3065ee8 100644
--- a/example/src/custom_appender.rs
+++ b/example/src/custom_appender.rs
@@ -6,7 +6,7 @@ use log::Level;
 struct CustomLog {}
 
 impl LogAppender for CustomLog {
-    fn do_logs(&self, records: &[FastLogRecord]) {
+    fn do_logs(&mut self, records: &[FastLogRecord]) {
         for record in records {
             let now = DateTime::from(record.now);
             let data;