diff --git a/Data/Yaml.hs b/Data/Yaml.hs
--- a/Data/Yaml.hs
+++ b/Data/Yaml.hs
@@ -86,6 +86,7 @@
 import qualified Data.HashMap.Strict as M
 import Data.Typeable
 import Data.Attoparsec.Number
+import qualified Data.HashSet as HashSet
 
 encode :: ToJSON a => a -> ByteString
 encode obj = unsafePerformIO $
@@ -123,7 +124,14 @@
 -- https://github.com/snoyberg/yaml/issues/24
 objToEvents' (String "") rest = EventScalar "" NoTag SingleQuoted Nothing : rest
 
-objToEvents' (String s) rest = EventScalar (encodeUtf8 s) StrTag PlainNoTag Nothing : rest
+objToEvents' (String s) rest =
+    event : rest
+  where
+    event
+        -- Make sure that special strings are encoded as strings properly.
+        -- See: https://github.com/snoyberg/yaml/issues/31
+        | s `HashSet.member` specialStrings = EventScalar (encodeUtf8 s) NoTag SingleQuoted Nothing
+        | otherwise = EventScalar (encodeUtf8 s) StrTag PlainNoTag Nothing
 objToEvents' Null rest = EventScalar "null" NullTag PlainNoTag Nothing : rest
 objToEvents' (Bool True) rest = EventScalar "true" BoolTag PlainNoTag Nothing : rest
 objToEvents' (Bool False) rest = EventScalar "false" BoolTag PlainNoTag Nothing : rest
@@ -133,6 +141,11 @@
 pairToEvents (k, v) rest =
     EventScalar (encodeUtf8 k) StrTag PlainNoTag Nothing
   : objToEvents' v rest
+
+-- | Strings which must be escaped so as not to be treated as non-string scalars.
+specialStrings :: HashSet.HashSet Text
+specialStrings = HashSet.fromList $ T.words
+    "y Y yes Yes YES n N no No NO true True TRUE false False FALSE on On ON off Off OFF null Null NULL ~"
 
 -- Parsing
 
diff --git a/test/main.hs b/test/main.hs
--- a/test/main.hs
+++ b/test/main.hs
@@ -116,6 +116,12 @@
                           , hash = HM.fromList [("key1", "value1"), ("key2", "value2")]
                           }
 
+    describe "round-tripping of special scalars" $ do
+        let special = words "y Y On ON false"
+        forM_ special $ \w -> it w $
+            let v = object ["word" .= w]
+             in D.decode (D.encode v) `shouldBe` Just v
+        it "no tags" $ D.encode (object ["word" .= ("true" :: String)]) `shouldBe` "word: 'true'\n"
 
 
 specialStrings :: [T.Text]
diff --git a/yaml.cabal b/yaml.cabal
--- a/yaml.cabal
+++ b/yaml.cabal
@@ -1,5 +1,5 @@
 name:            yaml
-version:         0.8.5
+version:         0.8.5.1
 license:         BSD3
 license-file:    LICENSE
 author:          Michael Snoyman <michael@snoyman.com>, Anton Ageev <antage@gmail.com>,Kirill Simonov