diff --git a/sys/bus/isa/pnp.c b/sys/bus/isa/pnp.c
--- a/sys/bus/isa/pnp.c
+++ b/sys/bus/isa/pnp.c
@@ -398,12 +398,14 @@
 			if (PNP_LRES_NUM(tag) == PNP_TAG_ID_ANSI) {
 				if (large_len > sizeof(buf) - 1)
 					large_len = sizeof(buf) - 1;
+				if (large_len == 0)
+					continue;
 				bcopy(resinfo, buf, large_len);
 
 				/*
 				 * Trim trailing spaces.
 				 */
-				while (buf[large_len-1] == ' ')
+				while (large_len > 0 && buf[large_len-1] == ' ')
 					large_len--;
 				buf[large_len] = '\0';
 				desc = buf;