diff --git a/lib/idr.c b/lib/idr.c
index e728c7f..7a785a0 100644
--- a/lib/idr.c
+++ b/lib/idr.c
@@ -185,6 +185,7 @@
 			new = get_from_free_list(idp);
 			if (!new)
 				return -1;
+			new->layer = l-1;
 			rcu_assign_pointer(p->ary[m], new);
 			p->count++;
 		}
@@ -210,6 +211,7 @@
 	if (unlikely(!p)) {
 		if (!(p = get_from_free_list(idp)))
 			return -1;
+		p->layer = 0;
 		layers = 1;
 	}
 	/*
@@ -237,6 +239,7 @@
 		}
 		new->ary[0] = p;
 		new->count = 1;
+		new->layer = layers-1;
 		if (p->bitmap == IDR_FULL)
 			__set_bit(0, &new->bitmap);
 		p = new;
@@ -493,17 +496,21 @@
 	int n;
 	struct idr_layer *p;
 
-	n = idp->layers * IDR_BITS;
 	p = rcu_dereference(idp->top);
+	if (!p)
+		return NULL;
+	n = (p->layer+1) * IDR_BITS;
 
 	/* Mask off upper bits we don't use for the search. */
 	id &= MAX_ID_MASK;
 
 	if (id >= (1 << n))
 		return NULL;
+	BUG_ON(n == 0);
 
 	while (n > 0 && p) {
 		n -= IDR_BITS;
+		BUG_ON(n != p->layer*IDR_BITS);
 		p = rcu_dereference(p->ary[(id >> n) & IDR_MASK]);
 	}
 	return((void *)p);
@@ -582,8 +589,11 @@
 	int n;
 	struct idr_layer *p, *old_p;
 
-	n = idp->layers * IDR_BITS;
 	p = idp->top;
+	if (!p)
+		return ERR_PTR(-EINVAL);
+
+	n = (p->layer+1) * IDR_BITS;
 
 	id &= MAX_ID_MASK;