diff --git a/code/acro.sty b/code/acro.sty
index 1a40b2b..8b3424a 100644
--- a/code/acro.sty
+++ b/code/acro.sty
@@ -243,6 +243,8 @@
 \clist_new:N \l__acro_tmpb_clist
 \clist_new:N \l__acro_tmpc_clist
 
+\prop_new:N \l__acro_tmpa_prop
+
 % ----------------------------------------------------------------------------
 % module mechanism:
 \msg_new:nnn {acro} {module-missing}