diff --git a/Lib/tkinter/__init__.py b/Lib/tkinter/__init__.py
index faca78f..bb014b3 100644
--- a/Lib/tkinter/__init__.py
+++ b/Lib/tkinter/__init__.py
@@ -1913,11 +1913,9 @@
             cnf = _cnfmerge((cnf, kw))
         self.widgetName = widgetName
         BaseWidget._setup(self, master, cnf)
-        classes = []
-        for k in cnf.keys():
-            if isinstance(k, type):
-                classes.append((k, cnf[k]))
-                del cnf[k]
+        classes = [(k, v) for k, v in cnf.items() if isinstance(k, type)]
+        for k, v in classes:
+            del cnf[k]
         self.tk.call(
             (widgetName, self._w) + extra + self._options(cnf))
         for k, v in classes:
diff --git a/Lib/tkinter/scrolledtext.py b/Lib/tkinter/scrolledtext.py
index 084c3bf..35767e6 100644
--- a/Lib/tkinter/scrolledtext.py
+++ b/Lib/tkinter/scrolledtext.py
@@ -19,11 +19,10 @@
             cnf = {}
         if kw:
             cnf = _cnfmerge((cnf, kw))
-        fcnf = {}
-        for k in cnf.keys():
-            if isinstance(k, type) or k == 'name':
-                fcnf[k] = cnf[k]
-                del cnf[k]
+        fcnf = {k:v for k,v in cnf.items() if isinstance(k,type) or k=='name'}
+        for k in fcnf.keys():
+            del cnf[k]
+
         self.frame = Frame(master, **fcnf)
         self.vbar = Scrollbar(self.frame, name='vbar')
         self.vbar.pack(side=RIGHT, fill=Y)
diff --git a/Misc/NEWS b/Misc/NEWS
index 3e77aa2..9bd063b 100644
--- a/Misc/NEWS
+++ b/Misc/NEWS
@@ -77,6 +77,9 @@
 Library
 -------
 
+- Issue #1658: tkinter changes dict size during iteration in both
+    tkinter.BaseWidget and tkinter.scrolledtext.ScrolledText.
+
 - The bsddb module (and therefore the dbm.bsd module) has been removed.
   It is now maintained outside of the standard library at
   http://www.jcea.es/programacion/pybsddb.htm.