diff --git a/README.txt b/README.txt
index f3f2945..18d909b 100644
--- a/README.txt
+++ b/README.txt
@@ -1,2 +1,4 @@
 sudo apt-get install python-nose python-coverage
-sudo apt-get install python-tables cython python-cherrypy3
+sudo apt-get install python-tables python-cherrypy3
+sudo apt-get install cython # 0.17.1-1 or newer
+
diff --git a/nilmdb/rbtree.py b/nilmdb/rbtree.pyx
similarity index 85%
rename from nilmdb/rbtree.py
rename to nilmdb/rbtree.pyx
index 029b86c..5dc79bf 100644
--- a/nilmdb/rbtree.py
+++ b/nilmdb/rbtree.pyx
@@ -1,4 +1,10 @@
-"""Red-black tree, where keys are stored as start/end timestamps.
+# cython: profile=False
+# cython: cdivision=True
+
+"""
+Jim Paris <jim@jtan.com>
+
+Red-black tree, where keys are stored as start/end timestamps.
 This is a basic interval tree that holds half-open intervals:
   [start, end)
 Intervals must not overlap.  Fixing that would involve making this
@@ -10,17 +16,21 @@ string 'non-overlapping'.
 
 import sys
 
-class RBNode(object):
+cdef class RBNode:
     """One node of the Red/Black tree, containing a key (start, end)
     and value (obj)"""
-    def __init__(self, start, end, obj = None):
+    cdef public object obj
+    cdef public double start, end
+    cdef public int red
+    cdef public RBNode left, right, parent
+
+    def __cinit__(RBNode self, double start, double end, object obj = None):
         self.obj = obj
         self.start = start
         self.end = end
         self.red = False
         self.left = None
         self.right = None
-        self.nil = False
 
     def __str__(self):
         if self.red:
@@ -34,11 +44,13 @@ class RBNode(object):
                 + str(self.start) + " -> " + str(self.end) + " "
                 + color + "]")
 
-class RBTree(object):
+cdef class RBTree:
     """Red/Black tree"""
 
+    cdef public RBNode nil, root
+
     # Init
-    def __init__(self):
+    def __cinit__(RBTree self):
         self.nil = RBNode(start = sys.float_info.min,
                           end = sys.float_info.min)
         self.nil.left = self.nil
@@ -53,11 +65,11 @@ class RBTree(object):
 
     # We have a dummy root node to simplify operations, so from an
     # external point of view, its left child is the real root.
-    def getroot(self):
+    cpdef getroot(RBTree self):
         return self.root.left
 
     # Rotations and basic operations
-    def __rotate_left(self, x):
+    cdef void __rotate_left(RBTree self, RBNode x):
         """Rotate left:
         #   x           y
         #  / \   -->   / \
@@ -65,7 +77,7 @@ class RBTree(object):
         #    / \     / \
         #   v   w   z   v
         """
-        y = x.right
+        cdef RBNode y = x.right
         x.right = y.left
         if y.left is not self.nil:
             y.left.parent = x
@@ -77,7 +89,7 @@ class RBTree(object):
         y.left = x
         x.parent = y
 
-    def __rotate_right(self, y):
+    cdef void __rotate_right(RBTree self, RBNode y):
         """Rotate right:
         #     y           x
         #    / \   -->   / \
@@ -85,7 +97,7 @@ class RBTree(object):
         #  / \             / \
         # z   v           v   w
         """
-        x = y.left
+        cdef RBNode x = y.left
         y.left = x.right
         if x.right is not self.nil:
             x.right.parent = y
@@ -97,9 +109,9 @@ class RBTree(object):
         x.right = y
         y.parent = x
 
-    def __successor(self, x):
+    cdef RBNode __successor(RBTree self, RBNode x):
         """Returns the successor of RBNode x"""
-        y = x.right
+        cdef RBNode y = x.right
         if y is not self.nil:
             while y.left is not self.nil:
                 y = y.left
@@ -111,14 +123,14 @@ class RBTree(object):
             if y is self.root:
                 return self.nil
         return y
-    def successor(self, x):
+    cpdef RBNode successor(RBTree self, RBNode x):
         """Returns the successor of RBNode x, or None"""
-        y = self.__successor(x)
+        cdef RBNode y = self.__successor(x)
         return y if y is not self.nil else None
 
-    def __predecessor(self, x):
+    cdef RBNode __predecessor(RBTree self, RBNode x):
         """Returns the predecessor of RBNode x"""
-        y = x.left
+        cdef RBNode y = x.left
         if y is not self.nil:
             while y.right is not self.nil:
                 y = y.right
@@ -131,18 +143,18 @@ class RBTree(object):
                 x = y
                 y = y.parent
         return y
-    def predecessor(self, x):
+    cpdef RBNode predecessor(RBTree self, RBNode x):
         """Returns the predecessor of RBNode x, or None"""
-        y = self.__predecessor(x)
+        cdef RBNode y = self.__predecessor(x)
         return y if y is not self.nil else None
 
     # Insertion
-    def insert(self, z):
+    cpdef insert(RBTree self, RBNode z):
         """Insert RBNode z into RBTree and rebalance as necessary"""
         z.left = self.nil
         z.right = self.nil
-        y = self.root
-        x = self.root.left
+        cdef RBNode y = self.root
+        cdef RBNode x = self.root.left
         while x is not self.nil:
             y = x
             if (x.start > z.start or (x.start == z.start and x.end > z.end)):
@@ -158,7 +170,7 @@ class RBTree(object):
         # relabel/rebalance
         self.__insert_fixup(z)
 
-    def __insert_fixup(self, x):
+    cdef void __insert_fixup(RBTree self, RBNode x):
         """Rebalance/fix RBTree after a simple insertion of RBNode x"""
         x.red = True
         while x.parent.red:
@@ -193,10 +205,11 @@ class RBTree(object):
         self.root.left.red = False
 
     # Deletion
-    def delete(self, z):
+    cpdef delete(RBTree self, RBNode z):
         if z.left is None or z.right is None:
             raise AttributeError("you can only delete a node object "
                                  + "from the tree; use find() to get one")
+        cdef RBNode x, y
         if z.left is self.nil or z.right is self.nil:
             y = z
         else:
@@ -233,10 +246,10 @@ class RBTree(object):
             if not y.red:
                 self.__delete_fixup(x)
 
-    def __delete_fixup(self, x):
+    cdef void __delete_fixup(RBTree self, RBNode x):
         """Rebalance/fix RBTree after a deletion.  RBNode x is the
         child of the spliced out node."""
-        rootLeft = self.root.left
+        cdef RBNode rootLeft = self.root.left
         while not x.red and x is not rootLeft:
             if x is x.parent.left:
                 w = x.parent.right
@@ -283,10 +296,10 @@ class RBTree(object):
         x.red = False
 
     # Walking, searching
-    def __iter__(self):
+    def __iter__(RBTree self):
         return self.inorder()
 
-    def inorder(self, x = None):
+    def inorder(RBTree self, RBNode x = None):
         """Generator that performs an inorder walk for the tree
         rooted at RBNode x"""
         if x is None:
@@ -297,9 +310,9 @@ class RBTree(object):
             yield x
             x = self.__successor(x)
 
-    def find(self, start, end):
+    cpdef RBNode find(RBTree self, double start, double end):
         """Return the node with exactly the given start and end."""
-        x = self.getroot()
+        cdef RBNode x = self.getroot()
         while x is not self.nil:
             if start < x.start:
                 x = x.left
@@ -314,14 +327,14 @@ class RBTree(object):
                 x = x.right
         return x if x is not self.nil else None
 
-    def find_left_end(self, t):
+    cpdef RBNode find_left_end(RBTree self, double t):
         """Find the leftmode node with end >= t.  With non-overlapping
         intervals, this is the first node that might overlap time t.
 
         Note that this relies on non-overlapping intervals, since
         it assumes that we can use the endpoints to traverse the
         tree even though it was created using the start points."""
-        x = self.getroot()
+        cdef RBNode x = self.getroot()
         while x is not self.nil:
             if t < x.end:
                 if x.left is self.nil:
@@ -336,10 +349,10 @@ class RBTree(object):
                 x = x.right
         return x if x is not self.nil else None
 
-    def find_right_start(self, t):
+    cpdef RBNode find_right_start(RBTree self, double t):
         """Find the rightmode node with start <= t.  With non-overlapping
         intervals, this is the last node that might overlap time t."""
-        x = self.getroot()
+        cdef RBNode x = self.getroot()
         while x is not self.nil:
             if t < x.start:
                 if x.left is self.nil:
@@ -355,11 +368,11 @@ class RBTree(object):
         return x if x is not self.nil else None
 
     # Intersections
-    def intersect(self, start, end):
+    def intersect(RBTree self, double start, double end):
         """Generator that returns nodes that overlap the given
         (start,end) range.  Assumes non-overlapping intervals."""
         # Start with the leftmode node that ends after start
-        n = self.find_left_end(start)
+        cdef RBNode n = self.find_left_end(start)
         while n is not None:
             if n.start >= end:
                 # this node starts after the requested end; we're done
diff --git a/setup.cfg b/setup.cfg
index 8c3fb3d..297fa82 100644
--- a/setup.cfg
+++ b/setup.cfg
@@ -12,6 +12,8 @@ stop=
 verbosity=2
 #tests=tests/test_cmdline.py
 #tests=tests/test_layout.py
+#tests=tests/test_rbtree.py
+#tests=tests/test_interval.py
 tests=tests/test_rbtree.py,tests/test_interval.py
 #tests=tests/test_interval.py
 #tests=tests/test_client.py
diff --git a/tests/test_rbtree.py b/tests/test_rbtree.py
index 08091c4..4e29ced 100644
--- a/tests/test_rbtree.py
+++ b/tests/test_rbtree.py
@@ -74,8 +74,8 @@ class TestRBTree:
         s = ""
         for node in rb:
             s += str(node)
-        assert "[node (None) 1 -> 1 B]" in s
-        assert str(rb.nil) == "[node nil]"
+        in_("[node (None) 1", s)
+        eq_(str(rb.nil), "[node nil]")
 
         # inorder traversal, successor and predecessor
         last = 0