diff -r d85efd73b0e1 Lib/curses/textpad.py
--- a/Lib/curses/textpad.py	Mon Dec 19 16:41:11 2011 -0500
+++ b/Lib/curses/textpad.py	Tue Dec 20 11:14:51 2011 -0600
@@ -43,20 +43,22 @@
     def __init__(self, win, insert_mode=False):
         self.win = win
         self.insert_mode = insert_mode
-        (self.maxy, self.maxx) = win.getmaxyx()
-        self.maxy = self.maxy - 1
-        self.maxx = self.maxx - 1
         self.stripspaces = 1
         self.lastcmd = None
         win.keypad(1)
 
+    def _getmaxyx(self):
+        (maxy, maxx) = self.win.getmaxyx()
+        return maxy-1, maxx-1
+
     def _end_of_line(self, y):
         """Go to the location of the first blank on the given line,
         returning the index of the last non-blank character."""
-        last = self.maxx
+        (maxy, maxx) = self._getmaxyx()
+        last = maxx
         while True:
             if curses.ascii.ascii(self.win.inch(y, last)) != curses.ascii.SP:
-                last = min(self.maxx, last+1)
+                last = min(maxx, last+1)
                 break
             elif last == 0:
                 break
@@ -65,9 +67,12 @@
 
     def _insert_printable_char(self, ch):
         (y, x) = self.win.getyx()
-        if y < self.maxy or x < self.maxx:
-            if self.insert_mode:
-                oldch = self.win.inch()
+        (maxy, maxx) = self._getmaxyx()
+        (backy, backx) = None, None
+
+        while y < maxy or x < maxx:
+            oldch = self.win.inch()
+
             # The try-catch ignores the error we trigger from some curses
             # versions by trying to write into the lowest-rightmost spot
             # in the window.
@@ -75,18 +80,27 @@
                 self.win.addch(ch)
             except curses.error:
                 pass
-            if self.insert_mode:
+
+            if not self.insert_mode or not curses.ascii.isprint(oldch):
+                break
+
+            # Remember where to put the cursor back since we are in insert_mode
+            if backy is None:
                 (backy, backx) = self.win.getyx()
-                if curses.ascii.isprint(oldch):
-                    self._insert_printable_char(oldch)
-                    self.win.move(backy, backx)
+
+            ch = oldch
+            (y, x) = self.win.getyx()
+
+        if self.insert_mode and backy:
+            self.win.move(backy, backx)
 
     def do_command(self, ch):
         "Process a single editing command."
+        (maxy, maxx) = self._getmaxyx()
         (y, x) = self.win.getyx()
         self.lastcmd = ch
         if curses.ascii.isprint(ch):
-            if y < self.maxy or x < self.maxx:
+            if y < maxy or x < maxx:
                 self._insert_printable_char(ch)
         elif ch == curses.ascii.SOH:                           # ^a
             self.win.move(y, 0)
@@ -98,7 +112,7 @@
             elif self.stripspaces:
                 self.win.move(y-1, self._end_of_line(y-1))
             else:
-                self.win.move(y-1, self.maxx)
+                self.win.move(y-1, maxx)
             if ch in (curses.ascii.BS, curses.KEY_BACKSPACE):
                 self.win.delch()
         elif ch == curses.ascii.EOT:                           # ^d
@@ -107,20 +121,20 @@
             if self.stripspaces:
                 self.win.move(y, self._end_of_line(y))
             else:
-                self.win.move(y, self.maxx)
+                self.win.move(y, maxx)
         elif ch in (curses.ascii.ACK, curses.KEY_RIGHT):       # ^f
-            if x < self.maxx:
+            if x < maxx:
                 self.win.move(y, x+1)
-            elif y == self.maxy:
+            elif y == maxy:
                 pass
             else:
                 self.win.move(y+1, 0)
         elif ch == curses.ascii.BEL:                           # ^g
             return 0
         elif ch == curses.ascii.NL:                            # ^j
-            if self.maxy == 0:
+            if maxy == 0:
                 return 0
-            elif y < self.maxy:
+            elif y < maxy:
                 self.win.move(y+1, 0)
         elif ch == curses.ascii.VT:                            # ^k
             if x == 0 and self._end_of_line(y) == 0:
@@ -132,7 +146,7 @@
         elif ch == curses.ascii.FF:                            # ^l
             self.win.refresh()
         elif ch in (curses.ascii.SO, curses.KEY_DOWN):         # ^n
-            if y < self.maxy:
+            if y < maxy:
                 self.win.move(y+1, x)
                 if x > self._end_of_line(y+1):
                     self.win.move(y+1, self._end_of_line(y+1))
@@ -148,16 +162,17 @@
     def gather(self):
         "Collect and return the contents of the window."
         result = ""
-        for y in range(self.maxy+1):
+        (maxy, maxx) = self._getmaxyx()
+        for y in range(maxy+1):
             self.win.move(y, 0)
             stop = self._end_of_line(y)
             if stop == 0 and self.stripspaces:
                 continue
-            for x in range(self.maxx+1):
+            for x in range(maxx+1):
                 if self.stripspaces and x > stop:
                     break
                 result = result + chr(curses.ascii.ascii(self.win.inch(y, x)))
-            if self.maxy > 0:
+            if maxy > 0:
                 result = result + "\n"
         return result
 
diff -r d85efd73b0e1 Lib/test/test_curses.py
--- a/Lib/test/test_curses.py	Mon Dec 19 16:41:11 2011 -0500
+++ b/Lib/test/test_curses.py	Tue Dec 20 11:14:51 2011 -0600
@@ -22,7 +22,7 @@
 # If either of these don't exist, skip the tests.
 curses = import_module('curses')
 curses.panel = import_module('curses.panel')
-
+curses.textpad = import_module('curses.textpad')
 
 # XXX: if newterm was supported we could use it instead of initscr and not exit
 term = os.environ.get('TERM')
@@ -269,9 +269,23 @@
     assert type(b) is bytes
     curses.putp(b)
 
+def test_issue13051(stdscr):
+    box = curses.textpad.Textbox(stdscr, insert_mode=True)
+    lines, cols = stdscr.getmaxyx()
+    stdscr.resize(lines-2, cols-2)
+
+    # this may cause infinite recursion, leading to a RuntimeError
+    box._insert_printable_char('a')
+
+    # clean up for other tests
+    stdscr.clear()
+
 def main(stdscr):
     curses.savetty()
     try:
+        # this test doesn't play nicely if there's random garbage on the
+        # screen, so we run it first
+        test_issue13051(stdscr)
         module_funcs(stdscr)
         window_funcs(stdscr)
         test_userptr_without_set(stdscr)
diff -r d85efd73b0e1 Misc/ACKS
--- a/Misc/ACKS	Mon Dec 19 16:41:11 2011 -0500
+++ b/Misc/ACKS	Tue Dec 20 11:14:51 2011 -0600
@@ -26,6 +26,7 @@
 Mark Anacker
 Shashwat Anand
 Anders Andersen
+Tycho Andersen
 John Anderson
 Erik Andersén
 Oliver Andrich