diff --git a/oec/tn3270.py b/oec/tn3270.py
index d079d05..2393f32 100644
--- a/oec/tn3270.py
+++ b/oec/tn3270.py
@@ -142,7 +142,9 @@ class TN3270Session(Session):
         self.telnet = None
 
     def _apply(self):
-        for (address, cell) in enumerate(self.emulator.cells):
+        for address in self.emulator.dirty:
+            cell = self.emulator.cells[address]
+
             byte = 0x00
 
             if isinstance(cell, AttributeCell):
@@ -152,6 +154,8 @@ class TN3270Session(Session):
 
             self.terminal.display.buffered_write(byte, index=address)
 
+        self.emulator.dirty.clear()
+
         # Update the message area.
         self.message_area = self._format_message_area()
 
diff --git a/requirements.txt b/requirements.txt
index 9e107e1..655f841 100644
--- a/requirements.txt
+++ b/requirements.txt
@@ -2,7 +2,7 @@ ptyprocess==0.6.0
 pycoax==0.1.2
 pyserial==3.4
 pyte==0.8.0
-pytn3270==0.1.0
+pytn3270==0.2.0
 sliplib==0.3.0
 sortedcontainers==2.1.0
 wcwidth==0.1.7
diff --git a/tests/test_tn3270.py b/tests/test_tn3270.py
index dc6581f..cd8a25c 100644
--- a/tests/test_tn3270.py
+++ b/tests/test_tn3270.py
@@ -49,6 +49,8 @@ class SessionHandleHostTestCase(unittest.TestCase):
         _set_attribute(cells, 104, MockAttribute(protected=True))
 
         self.session.emulator.cells = cells
+        self.session.emulator.dirty = set(range(105))
+
         self.session.emulator.cursor_address = 8
 
         # Act and assert
@@ -76,6 +78,7 @@ class SessionHandleHostTestCase(unittest.TestCase):
         self.session.emulator.update = Mock(return_value=True)
 
         self.session.emulator.cells = _create_screen_cells(24, 80)
+        self.session.emulator.dirty = set()
 
         # Act
         self.session.handle_host()
@@ -92,6 +95,7 @@ class SessionHandleKeyTestCase(unittest.TestCase):
         self.session.emulator = Mock()
 
         self.session.emulator.cells = []
+        self.session.emulator.dirty = set()
 
     def test_enter(self):
         # Act