diff --git a/skimage/graph/rag.py b/skimage/graph/rag.py
index 8f605b1e..26808b0a 100644
--- a/skimage/graph/rag.py
+++ b/skimage/graph/rag.py
@@ -15,6 +15,7 @@ from scipy.ndimage import filters
 from scipy import ndimage as nd
 import math
 from .. import draw, measure, segmentation, util, color
+import random
 try:
     from matplotlib import colors
     from matplotlib import cm
@@ -96,7 +97,10 @@ class RAG(nx.Graph):
         dst_nbrs = set(self.neighbors(dst))
         neighbors = (src_nbrs & dst_nbrs) - set([src, dst])
         if not in_place:
-            new = self.number_of_nodes() + 1
+            # Randomly select an id
+            new = random.randint(1, 99999999)
+            while new in self:
+                new = random.randint(1, 99999999)
             self.add_node(new)
 
         for neighbor in neighbors:
diff --git a/skimage/graph/tests/test_rag.py b/skimage/graph/tests/test_rag.py
index 04b82ff7..35eb5c38 100644
--- a/skimage/graph/tests/test_rag.py
+++ b/skimage/graph/tests/test_rag.py
@@ -41,10 +41,10 @@ def test_rag_merge():
     assert gc.edge[1][2]['weight'] == 20
     assert gc.edge[2][3]['weight'] == 40
 
-    g.merge_nodes(1, 4, in_place=True)
-    g.merge_nodes(2, 3, in_place=True)
-    g.merge_nodes(3, 4)
-    assert sorted(g.node[4]['labels']) == list(range(5))
+    g.merge_nodes(1, 4)
+    g.merge_nodes(2, 3)
+    n = g.merge_nodes(3, 4, in_place=False)
+    assert sorted(g.node[n]['labels']) == list(range(5))
     assert g.edges() == []