1 files changed, 5 insertions, 3 deletions
diff --git a/gowin/pack.cc b/gowin/pack.cc
index 0ba71705..fbd2092f 100644
--- a/gowin/pack.cc
+++ b/gowin/pack.cc
@@ -1033,9 +1033,11 @@ static void pack_io(Context *ctx)
             if (constr_bel != ci->attrs.end()) {
                 constr_bel_name = constr_bel->second.as_string();
             }
-            constr_bel = iob->attrs.find(id_BEL);
-            if (constr_bel != iob->attrs.end()) {
-                constr_bel_name = constr_bel->second.as_string();
+            if (iob != nullptr) {
+                constr_bel = iob->attrs.find(id_BEL);
+                if (constr_bel != iob->attrs.end()) {
+                    constr_bel_name = constr_bel->second.as_string();
+                }
             }
             if (!constr_bel_name.empty()) {
                 BelId constr_bel = ctx->getBelByNameStr(constr_bel_name);