diff --git a/.travis.yml b/.travis.yml
index 62b15ed..0ec2b91 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -8,5 +8,6 @@ install:
   - pip install six
   - pip install pycryptodome
   - pip install chardet
+  - pip install sortedcontainers
 script:
   nosetests --nologcapture
diff --git a/pdfminer/layout.py b/pdfminer/layout.py
index 587c221..ba9a2bf 100644
--- a/pdfminer/layout.py
+++ b/pdfminer/layout.py
@@ -1,9 +1,9 @@
+from sortedcontainers import SortedListWithKey
 
 from .utils import INF
 from .utils import Plane
 from .utils import get_bound
 from .utils import uniq
-from .utils import csort
 from .utils import fsplit
 from .utils import bbox2str
 from .utils import matrix2str
@@ -441,7 +441,7 @@ class LTTextBoxHorizontal(LTTextBox):
 
     def analyze(self, laparams):
         LTTextBox.analyze(self, laparams)
-        self._objs = csort(self._objs, key=lambda obj: -obj.y1)
+        self._objs.sort(key=lambda obj: -obj.y1)
         return
 
     def get_writing_mode(self):
@@ -452,7 +452,7 @@ class LTTextBoxVertical(LTTextBox):
 
     def analyze(self, laparams):
         LTTextBox.analyze(self, laparams)
-        self._objs = csort(self._objs, key=lambda obj: -obj.x1)
+        self._objs.sort(key=lambda obj: -obj.x1)
         return
 
     def get_writing_mode(self):
@@ -474,7 +474,7 @@ class LTTextGroupLRTB(LTTextGroup):
     def analyze(self, laparams):
         LTTextGroup.analyze(self, laparams)
         # reorder the objects from top-left to bottom-right.
-        self._objs = csort(self._objs, key=lambda obj:
+        self._objs.sort(key=lambda obj:
                            (1-laparams.boxes_flow)*(obj.x0) -
                            (1+laparams.boxes_flow)*(obj.y0+obj.y1))
         return
@@ -485,7 +485,7 @@ class LTTextGroupTBRL(LTTextGroup):
     def analyze(self, laparams):
         LTTextGroup.analyze(self, laparams)
         # reorder the objects from top-right to bottom-left.
-        self._objs = csort(self._objs, key=lambda obj:
+        self._objs.sort(key=lambda obj:
                            -(1+laparams.boxes_flow)*(obj.x0+obj.x1)
                            - (1-laparams.boxes_flow)*(obj.y1))
         return
@@ -639,21 +639,18 @@ class LTLayoutContainer(LTContainer):
             (c,d,_,_) = t
             return (c,d)
 
-        # XXX this still takes O(n^2)  :(
-        dists = []
+        dists = SortedListWithKey(key=key_obj)
         for i in range(len(boxes)):
             obj1 = boxes[i]
             for j in range(i+1, len(boxes)):
                 obj2 = boxes[j]
-                dists.append((0, dist(obj1, obj2), obj1, obj2))
-        # We could use dists.sort(), but it would randomize the test result.
-        dists = csort(dists, key=key_obj)
+                dists.add((0, dist(obj1, obj2), obj1, obj2))
         plane = Plane(self.bbox)
         plane.extend(boxes)
         while dists:
             (c, d, obj1, obj2) = dists.pop(0)
             if c == 0 and isany(obj1, obj2):
-                dists.append((1, d, obj1, obj2))
+                dists.add((1, d, obj1, obj2))
                 continue
             if (isinstance(obj1, (LTTextBoxVertical, LTTextGroupTBRL)) or
                 isinstance(obj2, (LTTextBoxVertical, LTTextGroupTBRL))):
@@ -662,11 +659,13 @@ class LTLayoutContainer(LTContainer):
                 group = LTTextGroupLRTB([obj1, obj2])
             plane.remove(obj1)
             plane.remove(obj2)
-            dists = [ (c,d,obj1,obj2) for (c,d,obj1,obj2) in dists
-                      if (obj1 in plane and obj2 in plane) ]
+            removed = [obj1, obj2]
+            to_remove = [ (c,d,obj1,obj2) for (c,d,obj1,obj2) in dists
+                      if (obj1 in removed or obj2 in removed) ]
+            for r in to_remove:
+                dists.remove(r)
             for other in plane:
-                dists.append((0, dist(group, other), group, other))
-            dists = csort(dists, key=key_obj)
+                dists.add((0, dist(group, other), group, other))
             plane.add(group)
         assert len(plane) == 1, str(len(plane))
         return list(plane)
diff --git a/pdfminer/utils.py b/pdfminer/utils.py
index 0e948c2..31c608a 100644
--- a/pdfminer/utils.py
+++ b/pdfminer/utils.py
@@ -145,13 +145,6 @@ def uniq(objs):
     return
 
 
-# csort
-def csort(objs, key):
-    """Order-preserving sorting function."""
-    idxs = dict((obj, i) for (i, obj) in enumerate(objs))
-    return sorted(objs, key=lambda obj: (key(obj), idxs[obj]))
-
-
 # fsplit
 def fsplit(pred, objs):
     """Split a list into two classes according to the predicate."""
diff --git a/setup.py b/setup.py
index 8eab391..dd9db18 100644
--- a/setup.py
+++ b/setup.py
@@ -3,7 +3,7 @@ import sys
 
 import pdfminer as package
 
-requires = ['six', 'pycryptodome']
+requires = ['six', 'pycryptodome', 'sortedcontainers']
 if sys.version_info >= (3, 0):
     requires.append('chardet')
 
diff --git a/tox.ini b/tox.ini
index cba1097..d0e167b 100644
--- a/tox.ini
+++ b/tox.ini
@@ -8,3 +8,4 @@ deps =
 	pycryptodome
 	chardet
 	nose
+	sortedcontainers