diff --git a/soundlib/ITCompression.cpp b/soundlib/ITCompression.cpp
index d83731b909..0908f94ab8 100644
--- a/soundlib/ITCompression.cpp
+++ b/soundlib/ITCompression.cpp
@@ -154,10 +154,11 @@ void ITCompression::CompressBlock(const typename Properties::sample_t *data, Smp
 	{
 		if(bwt[i] != width)
 		{
+			MPT_ASSERT(width >= 0);
 			if(width <= 6)
 			{
 				// Mode A: 1 to 6 bits
-				MPT_ASSERT(width);
+				MPT_ASSERT(width != 0);
 				WriteBits(width, (1 << (width - 1)));
 				WriteBits(Properties::fetchA, ConvertWidth(width, bwt[i]));
 			} else if(width < Properties::defWidth)