diff -r 1756beed417c Lib/curses/ascii.py
--- a/Lib/curses/ascii.py	Sat Dec 17 09:19:11 2016 +0100
+++ b/Lib/curses/ascii.py	Sat Dec 17 12:45:15 2016 +0200
@@ -53,19 +53,19 @@ def _ctoi(c):
 
 def isalnum(c): return isalpha(c) or isdigit(c)
 def isalpha(c): return isupper(c) or islower(c)
-def isascii(c): return _ctoi(c) <= 127          # ?
+def isascii(c): return 0 <= _ctoi(c) <= 127          # ?
 def isblank(c): return _ctoi(c) in (9, 32)
-def iscntrl(c): return _ctoi(c) <= 31 or _ctoi(c) == 127
-def isdigit(c): return _ctoi(c) >= 48 and _ctoi(c) <= 57
-def isgraph(c): return _ctoi(c) >= 33 and _ctoi(c) <= 126
-def islower(c): return _ctoi(c) >= 97 and _ctoi(c) <= 122
-def isprint(c): return _ctoi(c) >= 32 and _ctoi(c) <= 126
+def iscntrl(c): return 0 <= _ctoi(c) <= 31 or _ctoi(c) == 127
+def isdigit(c): return 48 <= _ctoi(c) <= 57
+def isgraph(c): return 33 <= _ctoi(c) <= 126
+def islower(c): return 97 <= _ctoi(c) <= 122
+def isprint(c): return 32 <= _ctoi(c) <= 126
 def ispunct(c): return isgraph(c) and not isalnum(c)
 def isspace(c): return _ctoi(c) in (9, 10, 11, 12, 13, 32)
-def isupper(c): return _ctoi(c) >= 65 and _ctoi(c) <= 90
+def isupper(c): return 65 <= _ctoi(c) <= 90
 def isxdigit(c): return isdigit(c) or \
-    (_ctoi(c) >= 65 and _ctoi(c) <= 70) or (_ctoi(c) >= 97 and _ctoi(c) <= 102)
-def isctrl(c): return _ctoi(c) < 32
+    (65 <= _ctoi(c) <= 70) or (97 <= _ctoi(c) <= 102)
+def isctrl(c): return 0 <= _ctoi(c) < 32
 def ismeta(c): return _ctoi(c) > 127
 
 def ascii(c):
diff -r 1756beed417c Lib/test/test_curses.py
--- a/Lib/test/test_curses.py	Sat Dec 17 09:19:11 2016 +0100
+++ b/Lib/test/test_curses.py	Sat Dec 17 12:45:15 2016 +0200
@@ -436,6 +436,25 @@ class TestAscii(unittest.TestCase):
             check(curses.ascii.ispunct, c in string.punctuation)
             check(curses.ascii.isxdigit, c in string.hexdigits)
 
+        for i in (-2, -1, 256, sys.maxunicode, sys.maxunicode+1):
+            self.assertFalse(curses.ascii.isalnum(i))
+            self.assertFalse(curses.ascii.isalpha(i))
+            self.assertFalse(curses.ascii.isdigit(i))
+            self.assertFalse(curses.ascii.islower(i))
+            self.assertFalse(curses.ascii.isspace(i))
+            self.assertFalse(curses.ascii.isupper(i))
+
+            self.assertFalse(curses.ascii.isascii(i))
+            self.assertFalse(curses.ascii.isctrl(i))
+            self.assertFalse(curses.ascii.iscntrl(i))
+            self.assertFalse(curses.ascii.isblank(i))
+            self.assertFalse(curses.ascii.isgraph(i))
+            self.assertFalse(curses.ascii.isprint(i))
+            self.assertFalse(curses.ascii.ispunct(i))
+            self.assertFalse(curses.ascii.isxdigit(i))
+
+        self.assertFalse(curses.ascii.ismeta(-1))
+
     def test_ascii(self):
         ascii = curses.ascii.ascii
         self.assertEqual(ascii('\xc1'), 'A')