diff --git a/Lib/tkinter/__init__.py b/Lib/tkinter/__init__.py
index 3bfeb7a017..ca8a124bb6 100644
--- a/Lib/tkinter/__init__.py
+++ b/Lib/tkinter/__init__.py
@@ -143,6 +143,22 @@ def _splitdict(tk, v, cut_minus=True, conv=None):
         dict[key] = value
     return dict
 
+def _setup_master(master=None):
+    """If master is not None, itself is returned. If master is None,
+    the default master is returned if there is one, otherwise a new
+    master is created and returned.
+
+    If it is not allowed to use the default root and master is None,
+    RuntimeError is raised."""
+    if master is None:
+        if _support_default_root:
+            master = _default_root or Tk()
+        else:
+            raise RuntimeError(
+                    "No master specified and tkinter is "
+                    "configured to not support default root")
+    return master
+
 
 class EventType(enum.StrEnum):
     KeyPress = '2'
@@ -329,8 +345,7 @@ def __init__(self, master=None, value=None, name=None):
         if name is not None and not isinstance(name, str):
             raise TypeError("name must be a string")
         global _varnum
-        if not master:
-            master = _default_root
+        master = _setup_master(master)
         self._root = master._root()
         self._tk = master.tk
         if name:
@@ -591,7 +606,7 @@ def get(self):
 
 def mainloop(n=0):
     """Run the main loop of Tcl."""
-    _default_root.tk.mainloop(n)
+    _setup_master().tk.mainloop(n)
 
 
 getint = int
@@ -602,7 +617,7 @@ def mainloop(n=0):
 def getboolean(s):
     """Convert true and false to integer values 1 and 0."""
     try:
-        return _default_root.tk.getboolean(s)
+        return _setup_master().tk.getboolean(s)
     except TclError:
         raise ValueError("invalid literal for getboolean()")
 
@@ -2521,13 +2536,7 @@ class BaseWidget(Misc):
 
     def _setup(self, master, cnf):
         """Internal function. Sets up information about children."""
-        if _support_default_root:
-            global _default_root
-            if not master:
-                if not _default_root:
-                    _default_root = Tk()
-                master = _default_root
-        self.master = master
+        self.master = master = _setup_master(master)
         self.tk = master.tk
         name = None
         if 'name' in cnf:
@@ -4146,11 +4155,13 @@ def __init__(self, name=None, cnf={}, master=None, **kw):
 
 
 def image_names():
-    return _default_root.tk.splitlist(_default_root.tk.call('image', 'names'))
+    master = _setup_master()
+    return master.tk.splitlist(master.tk.call('image', 'names'))
 
 
 def image_types():
-    return _default_root.tk.splitlist(_default_root.tk.call('image', 'types'))
+    master = _setup_master()
+    return master.tk.splitlist(master.tk.call('image', 'types'))
 
 
 class Spinbox(Widget, XView):
diff --git a/Lib/tkinter/ttk.py b/Lib/tkinter/ttk.py
index 968fd54dce..db14131520 100644
--- a/Lib/tkinter/ttk.py
+++ b/Lib/tkinter/ttk.py
@@ -27,6 +27,7 @@
 
 import tkinter
 from tkinter import _flatten, _join, _stringify, _splitdict
+from tkinter import _setup_master as setup_master
 
 # Verify if Tk is new enough to not need the Tile package
 _REQUIRE_TILE = True if tkinter.TkVersion < 8.5 else False
@@ -341,22 +342,6 @@ def tclobjs_to_py(adict):
 
     return adict
 
-def setup_master(master=None):
-    """If master is not None, itself is returned. If master is None,
-    the default master is returned if there is one, otherwise a new
-    master is created and returned.
-
-    If it is not allowed to use the default root and master is None,
-    RuntimeError is raised."""
-    if master is None:
-        if tkinter._support_default_root:
-            master = tkinter._default_root or tkinter.Tk()
-        else:
-            raise RuntimeError(
-                    "No master specified and tkinter is "
-                    "configured to not support default root")
-    return master
-
 
 class Style(object):
     """Manipulate style database."""