1 files changed, 7 insertions, 4 deletions
diff --git a/pez.c b/pez.c
index 40d097b..d965095 100644
--- a/pez.c
+++ b/pez.c
@@ -86,9 +86,11 @@ typedef struct Proto {
 typedef struct Upval Upval;
 struct Upval {
     OBJHEADER;
-    Upval *nextup;
     Val *ptr;
-    Val slot;
+    union {
+        Upval *nextup;
+        Val slot;
+    };
 };
 
 typedef struct Fn {
@@ -471,11 +473,12 @@ delproto(PezContext *cx, Proto *pr)
 static void
 closeups(PezContext *cx, Val *vals)
 {
-    for (Upval *up = cx->openup; up; up = up->nextup) {
+    for (Upval *up = cx->openup, *next; up; up = next) {
+        next = up->nextup;
         if (up->ptr >= vals) {
+            cx->openup = next;
             up->slot = *up->ptr;
             up->ptr = &up->slot;
-            cx->openup = up->nextup;
         }
     }
 }