diff --git a/v1.15-ruby3/Dockerfile b/v1.15-ruby3/Dockerfile
index 6194447..a1aec6e 100644
--- a/v1.15-ruby3/Dockerfile
+++ b/v1.15-ruby3/Dockerfile
@@ -1,4 +1,4 @@
-FROM alpine:3.17
+FROM alpine:3.18
 
 ENV FLUENTD_VERSION 1.15.3
 
diff --git a/v1.15-staging/Dockerfile b/v1.15-staging/Dockerfile
index 6194447..a1aec6e 100644
--- a/v1.15-staging/Dockerfile
+++ b/v1.15-staging/Dockerfile
@@ -1,4 +1,4 @@
-FROM alpine:3.17
+FROM alpine:3.18
 
 ENV FLUENTD_VERSION 1.15.3