diff --git a/gateware/sim/util/i2s.py b/gateware/sim/util/i2s.py
index ecc3ac3..bda3a78 100644
--- a/gateware/sim/util/i2s.py
+++ b/gateware/sim/util/i2s.py
@@ -21,13 +21,16 @@ async def i2s_clock_in_u32(bick, sdin):
 
 def bits_not(n, width):
     """Bitwise NOT from positive integer of `width` bits."""
+    n = int(n)
     return (1 << width) - 1 - n
 
 def bits_from_signed(n, width):
+    n = int(n)
     """Bits (2s complement) of `width` from signed integer."""
     return n if n >= 0 else bits_not(-n, width) + 1
 
 def signed_from_bits(n, width):
+    n = int(n)
     """Signed integer from (2s complement) bits of `width`."""
     if (1 << (width-1) & n) > 0:
         return -int(bits_not(n, width) + 1)