diff --git a/ext/bcmath/libbcmath/src/str2num.c b/ext/bcmath/libbcmath/src/str2num.c
index 79c1d4216fe..bd9a44a2405 100644
--- a/ext/bcmath/libbcmath/src/str2num.c
+++ b/ext/bcmath/libbcmath/src/str2num.c
@@ -180,7 +180,7 @@ bool bc_str2num(bc_num *num, const char *str, const char *end, size_t scale, siz
 			 */
 			if (str_scale > 0) {
 				const char *fractional_new_end = bc_skip_zero_reverse(fractional_end, fractional_ptr);
-				str_scale -= fractional_new_end - fractional_end;
+				str_scale -= fractional_end - fractional_new_end; /* fractional_end >= fractional_new_end */
 			}
 		}
 	} else {