diff --git a/ci/fmt.sh b/ci/fmt.sh
index 588510ba..4f750317 100755
--- a/ci/fmt.sh
+++ b/ci/fmt.sh
@@ -2,7 +2,7 @@
 set -eu
 cd -- "$(dirname "$0")/.."
 
-X_TOOLS_VERSION=v0.31.0
+X_TOOLS_VERSION=v0.40.0
 
 go mod tidy
 (cd ./internal/thirdparty && go mod tidy)
diff --git a/go.mod b/go.mod
index d32fbd77..9ba755a8 100644
--- a/go.mod
+++ b/go.mod
@@ -1,3 +1,3 @@
 module github.com/coder/websocket
 
-go 1.23
+go 1.25
diff --git a/internal/examples/go.mod b/internal/examples/go.mod
index e368b76b..65e05c2a 100644
--- a/internal/examples/go.mod
+++ b/internal/examples/go.mod
@@ -1,6 +1,6 @@
 module github.com/coder/websocket/examples
 
-go 1.23
+go 1.25
 
 replace github.com/coder/websocket => ../..
 
diff --git a/internal/thirdparty/go.mod b/internal/thirdparty/go.mod
index 7a86aca9..b714a490 100644
--- a/internal/thirdparty/go.mod
+++ b/internal/thirdparty/go.mod
@@ -1,6 +1,6 @@
 module github.com/coder/websocket/internal/thirdparty
 
-go 1.23
+go 1.25
 
 replace github.com/coder/websocket => ../..
 
diff --git a/stringer.go b/stringer.go
index 5a66ba29..ed7b12b8 100644
--- a/stringer.go
+++ b/stringer.go
@@ -50,11 +50,11 @@ const _MessageType_name = "MessageTextMessageBinary"
 var _MessageType_index = [...]uint8{0, 11, 24}
 
 func (i MessageType) String() string {
-	i -= 1
-	if i < 0 || i >= MessageType(len(_MessageType_index)-1) {
-		return "MessageType(" + strconv.FormatInt(int64(i+1), 10) + ")"
+	idx := int(i) - 1
+	if i < 1 || idx >= len(_MessageType_index)-1 {
+		return "MessageType(" + strconv.FormatInt(int64(i), 10) + ")"
 	}
-	return _MessageType_name[_MessageType_index[i]:_MessageType_index[i+1]]
+	return _MessageType_name[_MessageType_index[idx]:_MessageType_index[idx+1]]
 }
 func _() {
 	// An "invalid array index" compiler error signifies that the constant values have changed.
@@ -83,9 +83,9 @@ const _StatusCode_name = "StatusNormalClosureStatusGoingAwayStatusProtocolErrorS
 var _StatusCode_index = [...]uint16{0, 19, 34, 53, 74, 88, 106, 127, 156, 177, 196, 220, 239, 259, 278, 294, 312}
 
 func (i StatusCode) String() string {
-	i -= 1000
-	if i < 0 || i >= StatusCode(len(_StatusCode_index)-1) {
-		return "StatusCode(" + strconv.FormatInt(int64(i+1000), 10) + ")"
+	idx := int(i) - 1000
+	if i < 1000 || idx >= len(_StatusCode_index)-1 {
+		return "StatusCode(" + strconv.FormatInt(int64(i), 10) + ")"
 	}
-	return _StatusCode_name[_StatusCode_index[i]:_StatusCode_index[i+1]]
+	return _StatusCode_name[_StatusCode_index[idx]:_StatusCode_index[idx+1]]
 }