bplist: Silence compiler warning
diff --git a/src/bplist.c b/src/bplist.c
index ec4ebe2..23e28fe 100644
--- a/src/bplist.c
+++ b/src/bplist.c
@@ -740,8 +740,8 @@
     }
 
     /* store node_index for current recursion level */
-    if (ptr_array_size(bplist->used_indexes) < bplist->level+1) {
-        while (ptr_array_size(bplist->used_indexes) < bplist->level+1) {
+    if ((uint32_t)ptr_array_size(bplist->used_indexes) < bplist->level+1) {
+        while ((uint32_t)ptr_array_size(bplist->used_indexes) < bplist->level+1) {
             ptr_array_add(bplist->used_indexes, (void*)(uintptr_t)node_index);
         }
     } else {