diff --git a/cddl/contrib/opensolaris/tools/ctf/cvt/merge.c b/cddl/contrib/opensolaris/tools/ctf/cvt/merge.c
index 3dc2ad0cbda..aaf1382b1f1 100644
--- a/cddl/contrib/opensolaris/tools/ctf/cvt/merge.c
+++ b/cddl/contrib/opensolaris/tools/ctf/cvt/merge.c
@@ -179,11 +179,23 @@ struct merge_cb_data {
 static void
 add_mapping(alist_t *ta, tid_t srcid, tid_t tgtid)
 {
+	static int checkid = -1;
+
+	if (checkid == -1)
+		checkid = getenv("CTFMERGE_CHECKID") ? 1 : 0;
+
 	debug(3, "Adding mapping %u <%x> => %u <%x>\n", srcid, srcid, tgtid, tgtid);
 
 	assert(!alist_find(ta, (void *)(uintptr_t)srcid, NULL));
 	assert(srcid != 0 && tgtid != 0);
 
+	if (checkid) {
+		if (srcid > 32767)
+			aborterr("srcid overflow: %d\n", srcid);
+		if (tgtid > 32767)
+			aborterr("tgtid overflow: %d\n", tgtid);
+	}
+
 	alist_add(ta, (void *)(uintptr_t)srcid, (void *)(uintptr_t)tgtid);
 }