diff --git a/go.mod b/go.mod
index 4623c4cf..ffcc97c1 100644
--- a/go.mod
+++ b/go.mod
@@ -1,6 +1,6 @@
 module github.com/cybozu/assam
 
-go 1.12
+go 1.15
 
 require (
 	github.com/aws/aws-sdk-go v1.37.2