diff --git a/src/io.zig b/src/io.zig
index 88e1caa..58a3c38 100644
--- a/src/io.zig
+++ b/src/io.zig
@@ -10,7 +10,7 @@ pub const Writer = struct {
     writeContext: fn (*anyopaque, []const u8) usize,
 
     ///
-    ///
+    /// Radices supported by [writeInt].
     ///
     pub const Radix = enum {
         binary,
@@ -79,39 +79,45 @@ pub const Writer = struct {
         const Int = @TypeOf(value);
         const type_info = @typeInfo(Int);
 
-        if (type_info != .Int) @compileError("value must be of type int");
+        switch (type_info) {
+            .Int => {
+                if (value == 0) return writer.writeByte('0');
 
-        if (value == 0) return writer.writeByte('0');
+                // TODO: Unhardcode this as it will break with large ints.
+                var buffer = std.mem.zeroes([28]u8);
+                var buffer_count = @as(usize, 0);
+                var n1 = value;
 
-        // TODO: Unhardcode this as it will break with large ints.
-        var buffer = std.mem.zeroes([28]u8);
-        var buffer_count = @as(usize, 0);
-        var n1 = value;
+                if ((type_info.Int.signedness == .signed) and (value < 0)) {
+                    // Negative value.
+                    n1 = -value;
+                    buffer[0] = '-';
+                    buffer_count += 1;
+                }
 
-        if ((type_info.Int.signedness == .signed) and (value < 0)) {
-            // Negative value.
-            n1 = -value;
-            buffer[0] = '-';
-            buffer_count += 1;
+                while (n1 != 0) {
+                    const base = @enumToInt(radix);
+
+                    buffer[buffer_count] = @intCast(u8, (n1 % base) + '0');
+                    n1 = (n1 / base);
+                    buffer_count += 1;
+                }
+
+                for (buffer[0 .. (buffer_count / 2)]) |_, i|
+                    std.mem.swap(u8, &buffer[i], &buffer[buffer_count - i - 1]);
+
+                return (writer.write(buffer[0 .. buffer_count]) == buffer_count);
+            },
+
+            // Cast comptime int into known-size integer and try again.
+            .ComptimeInt => return writer.
+                writeInt(radix, @intCast(std.math.IntFittingRange(value, value), value)),
+
+            else => @compileError("value must be of type int"),
         }
-
-        while (n1 != 0) {
-            const base = @enumToInt(radix);
-
-            buffer[buffer_count] = @intCast(u8, (n1 % base) + '0');
-            n1 = (n1 / base);
-            buffer_count += 1;
-        }
-
-        for (buffer[0 .. (buffer_count / 2)]) |_, i|
-            std.mem.swap(u8, &buffer[i], &buffer[buffer_count - i - 1]);
-
-        return (writer.write(buffer[0 .. buffer_count]) == buffer_count);
     }
 };
 
-var null_context = @as(usize, 0);
-
 ///
 /// Writer that silently throws consumed data away and never fails.
 ///
@@ -119,13 +125,10 @@ var null_context = @as(usize, 0);
 /// sent somewhere for whatever reason.
 ///
 pub const null_writer = Writer{
-    .context = (&null_context),
-
-    .operation = struct {
-        fn write(context: *anyopaque, buffer: []const u8) usize {
-            // Validate context canary value.
-            std.debug.assert(@ptrCast(*usize, @alignCast(@alignOf(usize), context)).* == 0);
+    .context = undefined,
 
+    .writeContext = struct {
+        fn write(_: *anyopaque, buffer: []const u8) usize {
             return buffer.len;
         }
     }.write,
@@ -137,9 +140,9 @@ test {
     {
         const sequence = "foo";
 
-        testing.expectEqual(null_writer.write(sequence), sequence.len);
+        try testing.expectEqual(null_writer.write(sequence), sequence.len);
     }
 
-    testing.expect(null_writer.writeByte(0));
-    testing.expect(null_writer.writeInt(.decimal, 420));
+    try testing.expect(null_writer.writeByte(0));
+    try testing.expect(null_writer.writeInt(.decimal, 420));
 }