diff --git a/go.mod b/go.mod
index c4ad406..0824a96 100644
--- a/go.mod
+++ b/go.mod
@@ -4,5 +4,5 @@ go 1.25.0
 
 require (
 	github.com/toon-format/toon-go v0.0.0-20251202084852-7ca0e27c4e8c
-	golang.org/x/sync v0.20.0
+	golang.org/x/sync v0.21.0
 )
diff --git a/go.sum b/go.sum
index 6a182e6..662821c 100644
--- a/go.sum
+++ b/go.sum
@@ -1,4 +1,4 @@
 github.com/toon-format/toon-go v0.0.0-20251202084852-7ca0e27c4e8c h1:D8lDFovBMZywze1eh9iwMLcYor5f11mHBocLhO7cBe8=
 github.com/toon-format/toon-go v0.0.0-20251202084852-7ca0e27c4e8c/go.mod h1:j/BOnpF2ihnz4lELs99h9mwGJBx/zdleOUCnLLRPCsc=
-golang.org/x/sync v0.20.0 h1:e0PTpb7pjO8GAtTs2dQ6jYa5BWYlMuX047Dco/pItO4=
-golang.org/x/sync v0.20.0/go.mod h1:9xrNwdLfx4jkKbNva9FpL6vEN7evnE43NNNJQ2LF3+0=
+golang.org/x/sync v0.21.0 h1:HLII4xRRTtCRkxYp4HNFF0Js/Og6q2i++KXbg0gHCwM=
+golang.org/x/sync v0.21.0/go.mod h1:9xrNwdLfx4jkKbNva9FpL6vEN7evnE43NNNJQ2LF3+0=