diff --git a/README.md b/README.md
index 9572d9e..8142370 100644
--- a/README.md
+++ b/README.md
@@ -40,6 +40,7 @@ Save "Screen 0" to an .ans file.
 
 ## [SaveBinaryPBM.bm](https://github.com/visionmercer/qb64-include/blob/main/savebinarypbm.bm)
 Save a monochrome image to pbm file.
+Only works if width is divisible by 8.
 
 ## [SaveHexPalette](https://github.com/visionmercer/qb64-include/blob/main/savehexpalette.bm)
 Save an array of colors to file