diff --git a/libs/libc/obstack/lib_obstack_finish.c b/libs/libc/obstack/lib_obstack_finish.c
index 6c5fbcfc56..5cf1595b5a 100644
--- a/libs/libc/obstack/lib_obstack_finish.c
+++ b/libs/libc/obstack/lib_obstack_finish.c
@@ -66,10 +66,10 @@ FAR void *obstack_finish(FAR struct obstack *h)
     {
       chsize = h->next_free - (FAR char *)h->chunk;
       h->chunk = lib_obstack_realloc(h->chunk, chsize);
-      h->chunk->limit = (FAR void *)h->chunk + chsize;
+      h->chunk->limit = (FAR char *)h->chunk + chsize;
       h->object_base = h->chunk->limit;
       h->next_free = h->chunk->limit;
-      return (FAR void *)h->chunk + sizeof(struct _obstack_chunk);
+      return (FAR char *)h->chunk + sizeof(struct _obstack_chunk);
     }
 
   return obstack_finish_norealloc(h);
diff --git a/libs/libc/obstack/lib_obstack_free.c b/libs/libc/obstack/lib_obstack_free.c
index 460e27f054..6d5437de00 100644
--- a/libs/libc/obstack/lib_obstack_free.c
+++ b/libs/libc/obstack/lib_obstack_free.c
@@ -51,7 +51,8 @@ void obstack_free(FAR struct obstack *h, FAR void *object)
 
   while (h->chunk)
     {
-      if (object >= (FAR void *)&h->chunk + sizeof(struct _obstack_chunk)
+      if (object >=
+          (FAR void *)((FAR char *)&h->chunk + sizeof(struct _obstack_chunk))
           && object < (FAR void *)h->chunk->limit)
         {
           /* The object is in this chunk so just move object base.