diff --git a/Lib/idlelib/editor.py b/Lib/idlelib/editor.py
index 35027da..793ed3a 100644
--- a/Lib/idlelib/editor.py
+++ b/Lib/idlelib/editor.py
@@ -10,6 +10,7 @@
 import webbrowser
 
 from tkinter import *
+from tkinter.font import Font
 from tkinter.ttk import Scrollbar
 import tkinter.simpledialog as tkSimpleDialog
 import tkinter.messagebox as tkMessageBox
@@ -120,14 +121,13 @@
         self.prompt_last_line = ''  # Override in PyShell
         self.text_frame = text_frame = Frame(top)
         self.vbar = vbar = Scrollbar(text_frame, name='vbar')
-        self.width = idleConf.GetOption('main', 'EditorWindow',
-                                        'width', type='int')
+        width = idleConf.GetOption('main', 'EditorWindow', 'width', type='int')
         text_options = {
                 'name': 'text',
                 'padx': 5,
                 'wrap': 'none',
                 'highlightthickness': 0,
-                'width': self.width,
+                'width': width,
                 'tabstyle': 'wordprocessor',  # new in 8.5
                 'height': idleConf.GetOption(
                         'main', 'EditorWindow', 'height', type='int'),
@@ -154,6 +154,7 @@
         text.bind('<MouseWheel>', self.mousescroll)
         text.bind('<Button-4>', self.mousescroll)
         text.bind('<Button-5>', self.mousescroll)
+        text.bind('<Configure>', self.handle_winconfig)
         text.bind("<<cut>>", self.cut)
         text.bind("<<copy>>", self.copy)
         text.bind("<<paste>>", self.paste)
@@ -211,6 +212,7 @@
         text['font'] = idleConf.GetFont(self.root, 'main', 'EditorWindow')
         text.grid(row=1, column=1, sticky=NSEW)
         text.focus_set()
+        self.set_width()
 
         # usetabs true  -> literal tab characters are used by indent and
         #                  dedent cmds, possibly mixed with spaces if
@@ -338,6 +340,22 @@
         else:
             self.update_menu_state('options', '*Line Numbers', 'disabled')
 
+    def handle_winconfig(self, event=None):
+        self.set_width()
+
+    def set_width(self):
+        text = self.text
+        inner_padding = sum(map(text.tk.getint, [text.cget('border'),
+                                                 text.cget('padx')]))
+        pixel_width = text.winfo_width() - 2 * inner_padding
+
+        # Divide the width of the Text widget by the font width,
+        # which is taken to be the width of '0' (zero).
+        # http://www.tcl.tk/man/tcl8.6/TkCmd/text.htm#M21
+        zero_char_width = \
+            Font(text, font=text.cget('font')).measure('0')
+        self.width = pixel_width // zero_char_width
+
     def _filename_to_unicode(self, filename):
         """Return filename as BMP unicode so displayable in Tk."""
         # Decode bytes to unicode.
@@ -830,6 +848,7 @@
         # Finally, update the main text widget.
         new_font = idleConf.GetFont(self.root, 'main', 'EditorWindow')
         self.text['font'] = new_font
+        self.set_width()
 
     def RemoveKeybindings(self):
         "Remove the keybindings before they are changed."
diff --git a/Lib/idlelib/idle_test/test_squeezer.py b/Lib/idlelib/idle_test/test_squeezer.py
index 4e3da03..1af2ce8 100644
--- a/Lib/idlelib/idle_test/test_squeezer.py
+++ b/Lib/idlelib/idle_test/test_squeezer.py
@@ -82,18 +82,10 @@
 
 class SqueezerTest(unittest.TestCase):
     """Tests for the Squeezer class."""
-    def tearDown(self):
-        # Clean up the Squeezer class's reference to its instance,
-        # to avoid side-effects from one test case upon another.
-        if Squeezer._instance_weakref is not None:
-            Squeezer._instance_weakref = None
-
     def make_mock_editor_window(self, with_text_widget=False):
         """Create a mock EditorWindow instance."""
         editwin = NonCallableMagicMock()
-        # isinstance(editwin, PyShell) must be true for Squeezer to enable
-        # auto-squeezing; in practice this will always be true.
-        editwin.__class__ = PyShell
+        editwin.width = 80
 
         if with_text_widget:
             editwin.root = get_test_tk_root(self)
@@ -107,7 +99,6 @@
         if editor_window is None:
             editor_window = self.make_mock_editor_window()
         squeezer = Squeezer(editor_window)
-        squeezer.get_line_width = Mock(return_value=80)
         return squeezer
 
     def make_text_widget(self, root=None):
@@ -143,8 +134,8 @@
                               line_width=line_width,
                               expected=expected):
                 text = eval(text_code)
-                squeezer.get_line_width.return_value = line_width
-                self.assertEqual(squeezer.count_lines(text), expected)
+                with patch.object(editwin, 'width', line_width):
+                    self.assertEqual(squeezer.count_lines(text), expected)
 
     def test_init(self):
         """Test the creation of Squeezer instances."""
@@ -294,7 +285,6 @@
         """Test the reload() class-method."""
         editwin = self.make_mock_editor_window(with_text_widget=True)
         squeezer = self.make_squeezer_instance(editwin)
-        squeezer.load_font = Mock()
 
         orig_auto_squeeze_min_lines = squeezer.auto_squeeze_min_lines
 
@@ -307,7 +297,6 @@
         Squeezer.reload()
         self.assertEqual(squeezer.auto_squeeze_min_lines,
                          new_auto_squeeze_min_lines)
-        squeezer.load_font.assert_called()
 
     def test_reload_no_squeezer_instances(self):
         """Test that Squeezer.reload() runs without any instances existing."""
diff --git a/Lib/idlelib/squeezer.py b/Lib/idlelib/squeezer.py
index 032401f..be1538a 100644
--- a/Lib/idlelib/squeezer.py
+++ b/Lib/idlelib/squeezer.py
@@ -15,10 +15,8 @@
 messages and their tracebacks.
 """
 import re
-import weakref
 
 import tkinter as tk
-from tkinter.font import Font
 import tkinter.messagebox as tkMessageBox
 
 from idlelib.config import idleConf
@@ -203,8 +201,6 @@
     This avoids IDLE's shell slowing down considerably, and even becoming
     completely unresponsive, when very long outputs are written.
     """
-    _instance_weakref = None
-
     @classmethod
     def reload(cls):
         """Load class variables from config."""
@@ -213,14 +209,6 @@
             type="int", default=50,
         )
 
-        # Loading the font info requires a Tk root. IDLE doesn't rely
-        # on Tkinter's "default root", so the instance will reload
-        # font info using its editor windows's Tk root.
-        if cls._instance_weakref is not None:
-            instance = cls._instance_weakref()
-            if instance is not None:
-                instance.load_font()
-
     def __init__(self, editwin):
         """Initialize settings for Squeezer.
 
@@ -241,9 +229,6 @@
         # however, needs to make such changes.
         self.base_text = editwin.per.bottom
 
-        Squeezer._instance_weakref = weakref.ref(self)
-        self.load_font()
-
         # Twice the text widget's border width and internal padding;
         # pre-calculated here for the get_line_width() method.
         self.window_width_delta = 2 * (
@@ -298,24 +283,7 @@
 
         Tabs are considered tabwidth characters long.
         """
-        linewidth = self.get_line_width()
-        return count_lines_with_wrapping(s, linewidth)
-
-    def get_line_width(self):
-        # The maximum line length in pixels: The width of the text
-        # widget, minus twice the border width and internal padding.
-        linewidth_pixels = \
-            self.base_text.winfo_width() - self.window_width_delta
-
-        # Divide the width of the Text widget by the font width,
-        # which is taken to be the width of '0' (zero).
-        # http://www.tcl.tk/man/tcl8.6/TkCmd/text.htm#M21
-        return linewidth_pixels // self.zero_char_width
-
-    def load_font(self):
-        text = self.base_text
-        self.zero_char_width = \
-            Font(text, font=text.cget('font')).measure('0')
+        return count_lines_with_wrapping(s, self.editwin.width)
 
     def squeeze_current_text_event(self, event):
         """squeeze-current-text event handler