--- a/sys/libprop/prop_dictionary.c
+++ b/sys/libprop/prop_dictionary.c
@@ -1336,6 +1336,9 @@
 					&ctx->poic_cp) == false)
 		goto bad;
 
+	if (keylen == 0)	/* keysyms must be non-empty */
+		goto bad;
+
 	_PROP_ASSERT(keylen <= PDK_MAXKEY);
 	tmpkey[keylen] = '\0';