diff --git a/lib/yaml/reader.py b/lib/yaml/reader.py
index b2f10b09..4b377d61 100644
--- a/lib/yaml/reader.py
+++ b/lib/yaml/reader.py
@@ -139,7 +139,7 @@ def determine_encoding(self):
     if has_ucs4:
         NON_PRINTABLE = re.compile(u'[^\x09\x0A\x0D\x20-\x7E\x85\xA0-\uD7FF\uE000-\uFFFD\U00010000-\U0010ffff]')
     else:
-        NON_PRINTABLE = re.compile(u'[^\x09\x0A\x0D\x20-\x7E\x85\xA0-\uD7FF\uE000-\uFFFD]')
+        NON_PRINTABLE = re.compile(u'[^\x09\x0A\x0D\x20-\x7E\x85\xA0-\uFFFD]|(?:^|[^\uD800-\uDBFF])[\uDC00-\uDFFF]|[\uD800-\uDBFF](?:[^\uDC00-\uDFFF]|$)')
     def check_printable(self, data):
         match = self.NON_PRINTABLE.search(data)
         if match: