diff --git a/src/util/DateTime.zig b/src/util/DateTime.zig
index 199cdc3..2b096fa 100644
--- a/src/util/DateTime.zig
+++ b/src/util/DateTime.zig
@@ -117,14 +117,16 @@ pub fn toCharArrayZ(value: DateTime) [array_len + 1:0]u8 {
     return buf;
 }
 
-pub fn format(value: DateTime, comptime _: []const u8, _: std.fmt.FormatOptions, writer: anytype) !void {
-    return std.fmt.format(
-        writer,
-        "{:0>4}-{:0>2}-{:0>2}T{:0>2}:{:0>2}:{:0>2}Z",
-        .{ value.year(), value.month().numeric(), value.day(), value.hour(), value.minute(), value.second() },
-    );
+pub fn format(value: DateTime, comptime fmt: []const u8, _: std.fmt.FormatOptions, writer: anytype) !void {
+    if (comptime std.ascii.eqlIgnoreCase(fmt, "rfc3339") or fmt.len == 0) {
+        return std.fmt.format(
+            writer,
+            "{:0>4}-{:0>2}-{:0>2}T{:0>2}:{:0>2}:{:0>2}Z",
+            .{ value.year(), value.month().numeric(), value.day(), value.hour(), value.minute(), value.second() },
+        );
+    } else @compileError("Unknown DateTime format " ++ fmt);
 }
 
 pub fn jsonStringify(value: DateTime, _: std.json.StringifyOptions, writer: anytype) !void {
-    try std.fmt.format(writer, "\"{}\"", .{value});
+    try std.fmt.format(writer, "\"{rfc3339}\"", .{value});
 }