diff --git a/go.mod b/go.mod
index 8cc56600705f6a34aff61dedcc1a04b164a27db0..453b51ed285936b6187ea630592e2b97f8026efb 100644
--- a/go.mod
+++ b/go.mod
@@ -7,5 +7,5 @@ require (
 	github.com/jhillyerd/enmime v1.0.1
 	github.com/oschwald/geoip2-golang v1.9.0
 	github.com/prometheus/client_golang v1.11.0
-	golang.org/x/sync v0.3.0
+	golang.org/x/sync v0.4.0
 )
diff --git a/go.sum b/go.sum
index fa8615d5f2ceb20e370a468c372f2963ad2c1754..5c631a1b50fc083b3da1d83fc4a0e853741eeb41 100644
--- a/go.sum
+++ b/go.sum
@@ -200,6 +200,8 @@ golang.org/x/sync v0.1.0 h1:wsuoTGHzEhffawBOhz5CYhcrV4IdKZbEyZjBMuTp12o=
 golang.org/x/sync v0.1.0/go.mod h1:RxMgew5VJxzue5/jJTE5uejpjVlOe/izrB70Jof72aM=
 golang.org/x/sync v0.3.0 h1:ftCYgMx6zT/asHUrPw8BLLscYtGznsLAnjq5RH9P66E=
 golang.org/x/sync v0.3.0/go.mod h1:FU7BRWz2tNW+3quACPkgCx/L+uEAv1htQ0V83Z9Rj+Y=
+golang.org/x/sync v0.4.0 h1:zxkM55ReGkDlKSM+Fu41A+zmbZuaPVbGMzvvdUPznYQ=
+golang.org/x/sync v0.4.0/go.mod h1:FU7BRWz2tNW+3quACPkgCx/L+uEAv1htQ0V83Z9Rj+Y=
 golang.org/x/sys v0.0.0-20180905080454-ebe1bf3edb33/go.mod h1:STP8DvDyc/dI5b8T5hshtkjS+E42TnysNCUPdjciGhY=
 golang.org/x/sys v0.0.0-20181116152217-5ac8a444bdc5/go.mod h1:STP8DvDyc/dI5b8T5hshtkjS+E42TnysNCUPdjciGhY=
 golang.org/x/sys v0.0.0-20190215142949-d0b11bdaac8a/go.mod h1:STP8DvDyc/dI5b8T5hshtkjS+E42TnysNCUPdjciGhY=