diff --git a/cddl/contrib/opensolaris/common/ctf/ctf_lookup.c b/cddl/contrib/opensolaris/common/ctf/ctf_lookup.c
--- a/cddl/contrib/opensolaris/common/ctf/ctf_lookup.c
+++ b/cddl/contrib/opensolaris/common/ctf/ctf_lookup.c
@@ -132,8 +132,9 @@
 			continue; /* skip qualifier keyword */
 
 		for (lp = fp->ctf_lookups; lp->ctl_prefix != NULL; lp++) {
-			if (lp->ctl_prefix[0] == '\0' ||
-			    strncmp(p, lp->ctl_prefix, (size_t)(q - p)) == 0) {
+			if ((size_t)(q - p) >= lp->ctl_len &&
+			    (lp->ctl_prefix[0] == '\0' ||
+			    strncmp(p, lp->ctl_prefix, (size_t)(q - p)) == 0)) {
 				for (p += lp->ctl_len; isspace(*p); p++)
 					continue; /* skip prefix and next ws */