diff --git a/src/charset.c b/src/charset.c
index 34751e1..203a8fe 100644
--- a/src/charset.c
+++ b/src/charset.c
@@ -2002,6 +2002,7 @@
 	}
 	else
 	{
+	    // prevent a larg unsigned number to become negative
 	    if (un > VARNUM_MAX)
 		un = VARNUM_MAX;
 	    *nptr = (varnumber_T)un;