diff --git a/pydot_ng/__init__.py b/pydot_ng/__init__.py
index 1c4e4d1..7f97ccd 100644
--- a/pydot_ng/__init__.py
+++ b/pydot_ng/__init__.py
@@ -198,15 +198,13 @@ class frozendict(dict):
         return "frozendict(%s)" % dict.__repr__(self)
 
 
-dot_keywords = ['graph', 'subgraph', 'digraph', 'node', 'edge', 'strict']
-
-id_re_alpha_nums = re.compile('^[_a-zA-Z][a-zA-Z0-9_,]*$', re.UNICODE)
-id_re_alpha_nums_with_ports = re.compile(
-    '^[_a-zA-Z][a-zA-Z0-9_,:\"]*[a-zA-Z0-9_,\"]+$', re.UNICODE)
-id_re_num = re.compile('^[0-9,]+$', re.UNICODE)
-id_re_with_port = re.compile('^([^:]*):([^:]*)$', re.UNICODE)
-id_re_dbl_quoted = re.compile('^\".*\"$', re.S | re.UNICODE)
-id_re_html = re.compile('^<.*>$', re.S | re.UNICODE)
+# cases when no qoutes needed, from http://www.graphviz.org/doc/info/lang.html
+dot_keywords = ('graph', 'subgraph', 'digraph', 'node', 'edge', 'strict')
+id_alpha_num = re.compile(r'^[_a-zA-Z\200-\377][_a-zA-Z0-9\200-\377]*$',
+                          re.UNICODE)
+id_num = re.compile(r'^[-]?(\.[0-9]+|[0-9]+(\.[0-9]*)?)$', re.UNICODE)
+id_html = re.compile(r'^<.*>$', re.DOTALL | re.UNICODE)
+id_quoted = re.compile(r'^".*"$', re.DOTALL | re.UNICODE)
 
 
 def needs_quotes(s):
@@ -228,19 +226,18 @@ def needs_quotes(s):
     if s in dot_keywords:
         return False
 
-    chars = [ord(c) for c in s if ord(c) > 0x7f or ord(c) == 0]
-    if chars and not id_re_dbl_quoted.match(s) and not id_re_html.match(s):
-        return True
-
     for test_re in [
-            id_re_alpha_nums, id_re_num, id_re_dbl_quoted,
-            id_re_html, id_re_alpha_nums_with_ports]:
+        id_alpha_num,
+        id_num,
+        id_html,
+        id_quoted,
+    ]:
         if test_re.match(s):
             return False
 
-    m = id_re_with_port.match(s)
-    if m:
-        return needs_quotes(m.group(1)) or needs_quotes(m.group(2))
+    chars = [ord(c) for c in s if ord(c) > 0x7f or ord(c) == 0]
+    if chars and not id_quoted.match(s) and not id_html.match(s):
+        return True
 
     return True
 
diff --git a/test/test_pydot.py b/test/test_pydot.py
index 409d6dc..51f3329 100644
--- a/test/test_pydot.py
+++ b/test/test_pydot.py
@@ -285,6 +285,33 @@ class TestGraphAPI(unittest.TestCase):
         data = g.create(format='jpe')
         self.assertEqual(len(data) > 0, True)
 
+
+class TestQuoting(unittest.TestCase):
+
+    def test_quote_cases(self):
+        checks = (
+            ('A:', '"A:"'),
+            (':B', '":B"'),
+            ('A:B', '"A:B"'),
+            ('1A', '"1A"'),
+            ('A', 'A'),
+            ('11', '11'),
+            ('_xyz', '_xyz'),
+            ('.11', '.11'),
+            ('-.09', '-.09'),
+            ('1.8', '1.8'),
+            ('', '""'),
+            ('"1abc"', '"1abc"'),
+            ('@', '"@"'),
+            ('ÿ', 'ÿ'),
+            ('$GUID__/ffb73e1c-7495-40b3-9618-9e5462fc89c7',
+             '"$GUID__/ffb73e1c-7495-40b3-9618-9e5462fc89c7"')
+        )
+
+        for input, expected in checks:
+            self.assertEqual(pydot.quote_if_necessary(input), expected)
+
+
 if __name__ == '__main__':
     suite = unittest.TestLoader().loadTestsFromTestCase(TestGraphAPI)
     unittest.TextTestRunner(verbosity=2).run(suite)