--- yasm-0.4.0/modules/preprocs/nasm/genmacro.c~	2004-10-31 03:55:54.000000000 +0000
+++ yasm-0.4.0/modules/preprocs/nasm/genmacro.c	2005-02-14 09:21:37.000000000 +0000
@@ -102,8 +102,8 @@
 	    while (*strp == ' ' || *strp == '\t')
 		strp++;
 	    len = strlen(strp);
-	    while (strp[len-1] == ' ' || strp[len-1] == '\t' ||
-		   strp[len-1] == '\n') {
+	    while (len && (strp[len-1] == ' ' || strp[len-1] == '\t' ||
+			   strp[len-1] == '\n')) {
 		strp[len-1] = '\0';
 		len--;
 	    }