diff --git a/Data/Yaml.hs b/Data/Yaml.hs
--- a/Data/Yaml.hs
+++ b/Data/Yaml.hs
@@ -134,7 +134,7 @@
     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
+        | s `HashSet.member` specialStrings || isNumeric s = 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
@@ -150,6 +150,16 @@
 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 ~"
+
+isNumeric :: Text -> Bool
+isNumeric =
+    T.all isNumeric'
+  where
+    isNumeric' c = ('0' <= c && c <= '9')
+                || c == 'e'
+                || c == 'E'
+                || c == '.'
+                || c == '-'
 
 -- Parsing
 
diff --git a/test/main.hs b/test/main.hs
--- a/test/main.hs
+++ b/test/main.hs
@@ -124,7 +124,7 @@
                           }
 
     describe "round-tripping of special scalars" $ do
-        let special = words "y Y On ON false"
+        let special = words "y Y On ON false 12345 12345.0 12345a 12e3"
         forM_ special $ \w -> it w $
             let v = object ["word" .= w]
              in D.decode (D.encode v) `shouldBe` Just v
diff --git a/yaml.cabal b/yaml.cabal
--- a/yaml.cabal
+++ b/yaml.cabal
@@ -1,5 +1,5 @@
 name:            yaml
-version:         0.8.6
+version:         0.8.6.1
 license:         BSD3
 license-file:    LICENSE
 author:          Michael Snoyman <michael@snoyman.com>, Anton Ageev <antage@gmail.com>,Kirill Simonov