diff --git a/coderd/httpapi/httpapi.go b/coderd/httpapi/httpapi.go
index 942419182dfc1..e0f510b372276 100644
--- a/coderd/httpapi/httpapi.go
+++ b/coderd/httpapi/httpapi.go
@@ -182,7 +182,7 @@ func WebsocketCloseSprintf(format string, vars ...any) string {
 	if len(msg) > websocketCloseMaxLen {
 		// Trim the string to 123 bytes. If we accidentally cut in the middle of
 		// a UTF-8 character, remove it from the string.
-		return strings.ToValidUTF8(string(msg[123]), "")
+		return strings.ToValidUTF8(msg[:websocketCloseMaxLen], "")
 	}
 
 	return msg
diff --git a/coderd/httpapi/httpapi_test.go b/coderd/httpapi/httpapi_test.go
index 77ff9cdca6fd6..ea6d5a92ea5be 100644
--- a/coderd/httpapi/httpapi_test.go
+++ b/coderd/httpapi/httpapi_test.go
@@ -4,6 +4,7 @@ import (
 	"bytes"
 	"context"
 	"encoding/json"
+	"fmt"
 	"net/http"
 	"net/http/httptest"
 	"strings"
@@ -122,15 +123,28 @@ func TestRead(t *testing.T) {
 	})
 }
 
-func WebsocketCloseMsg(t *testing.T) {
+func TestWebsocketCloseMsg(t *testing.T) {
 	t.Parallel()
 
+	t.Run("Sprintf", func(t *testing.T) {
+		t.Parallel()
+
+		var (
+			msg  = "this is my message %q %q"
+			opts = []any{"colin", "kyle"}
+		)
+
+		expected := fmt.Sprintf(msg, opts...)
+		got := httpapi.WebsocketCloseSprintf(msg, opts...)
+		assert.Equal(t, expected, got)
+	})
+
 	t.Run("TruncateSingleByteCharacters", func(t *testing.T) {
 		t.Parallel()
 
 		msg := strings.Repeat("d", 255)
 		trunc := httpapi.WebsocketCloseSprintf(msg)
-		assert.LessOrEqual(t, len(trunc), 123)
+		assert.Equal(t, len(trunc), 123)
 	})
 
 	t.Run("TruncateMultiByteCharacters", func(t *testing.T) {
@@ -138,6 +152,6 @@ func WebsocketCloseMsg(t *testing.T) {
 
 		msg := strings.Repeat("こんにちは", 10)
 		trunc := httpapi.WebsocketCloseSprintf(msg)
-		assert.LessOrEqual(t, len(trunc), 123)
+		assert.Equal(t, len(trunc), 123)
 	})
 }