diff --git a/prism/util/pm_constant_pool.c b/prism/util/pm_constant_pool.c
index 624002cec9..38ea01a228 100644
--- a/prism/util/pm_constant_pool.c
+++ b/prism/util/pm_constant_pool.c
@@ -15,8 +15,12 @@ pm_constant_id_list_init(pm_constant_id_list_t *list) {
  */
 void
 pm_constant_id_list_init_capacity(pm_constant_id_list_t *list, size_t capacity) {
-    list->ids = xcalloc(capacity, sizeof(pm_constant_id_t));
-    if (list->ids == NULL) abort();
+    if (capacity) {
+        list->ids = xcalloc(capacity, sizeof(pm_constant_id_t));
+        if (list->ids == NULL) abort();
+    } else {
+        list->ids = NULL;
+    }
 
     list->size = 0;
     list->capacity = capacity;