diff --git a/src/padding.zig b/src/padding.zig
index 66ff91e..df8017c 100644
--- a/src/padding.zig
+++ b/src/padding.zig
@@ -1,4 +1,5 @@
 const std = @import("std");
+const assert = std.debug.assert;
 
 // rounds up a u12 to the nearest factor of 4 and returns the difference
 // (padding)
@@ -8,6 +9,7 @@ pub fn roundUpPadding(comptime T: type, comptime nbits: u8, n: T) T {
 
 // rounds up a u12 to the nearest factor of 4.
 pub fn roundUp(comptime T: type, comptime nbits: u8, n: T) T {
+    comptime assert(nbits < @bitSizeOf(T));
     const factor = comptime (1 << nbits) - 1;
     return ((n + factor) & ~@as(T, factor));
 }