diff --git a/module/unicode/u8_textprep.c b/module/unicode/u8_textprep.c
index 1940ee510d2c..3be37d293377 100644
--- a/module/unicode/u8_textprep.c
+++ b/module/unicode/u8_textprep.c
@@ -1287,7 +1287,7 @@ do_composition(size_t uv, uchar_t *s, uchar_t *comb_class, uchar_t *start,
 
 		while (p < oslast) {
 			size = u8_number_of_bytes[*p];
-			if (size <= 1 || (p + size) > oslast)
+			if ((ssize_t)size <= 1 || (p + size) > oslast)
 				break;
 
 			saved_p = p;