diff --git a/CHANGELOG.md b/CHANGELOG.md
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -1,5 +1,13 @@
 # Changelog
 
+## 1.0.2.0 - 2019-10-15
+
+### Changed
+
+  - Only quote YAML 1.2 boolean strings "true" and "false" (upper or
+    lowercase), not "on", "off", "yes", "y", "no", "n" (if you want to quote
+    these strings, use `encodeQuoted`.
+
 ## 1.0.1.0 - 2019-10-15
 
 ### Added
diff --git a/aeson-yaml.cabal b/aeson-yaml.cabal
--- a/aeson-yaml.cabal
+++ b/aeson-yaml.cabal
@@ -1,7 +1,7 @@
 cabal-version: 1.12
 
 name:           aeson-yaml
-version:        1.0.1.0
+version:        1.0.2.0
 homepage:       https://github.com/clovyr/aeson-yaml
 bug-reports:    https://github.com/clovyr/aeson-yaml/issues
 author:         Patrick Nielsen
diff --git a/src/Data/Aeson/Yaml.hs b/src/Data/Aeson/Yaml.hs
--- a/src/Data/Aeson/Yaml.hs
+++ b/src/Data/Aeson/Yaml.hs
@@ -121,21 +121,15 @@
   where
     unquotable =
       s /= "" &&
-      (not $ isSpecial s) &&
+      not isSpecial &&
       isSafeAscii (Text.head s) &&
       not (Text.all isNumberRelated s) && Text.all isAllowed s
-    isSpecial s'
+    isSpecial
       | Text.length s > 5 = False
       | otherwise =
-        case Text.toLower s' of
+        case Text.toLower s of
           "true" -> True
           "false" -> True
-          "on" -> True
-          "off" -> True
-          "y" -> True
-          "yes" -> True
-          "n" -> True
-          "no" -> True
           _ -> False
     isSafeAscii c =
       (c >= 'a' && c <= 'z') ||
diff --git a/test/Test/Data/Aeson/Yaml.hs b/test/Test/Data/Aeson/Yaml.hs
--- a/test/Test/Data/Aeson/Yaml.hs
+++ b/test/Test/Data/Aeson/Yaml.hs
@@ -40,12 +40,11 @@
    "isFalse": false,
    "numberString": "12345",
    "quoted ! key": true,
-   "ON": "ON",
-   "off": "off",
+   "boolString": "true",
    "piString": "3.14",
    "expString": "1e3",
    "multiLine": "The first line is followed by the\nsecond line\n",
-   "multiLineWithSpaces": "  This has\nextra spaces at the beginning\n",
+   "multiLineWithSpaces": "         This has extra\n     spaces at the beginning\n",
    "notMultiline": "This won't be\nmulti-lined",
    "apiVersion": "apps/v1",
    "kind": "Deployment",
@@ -102,8 +101,8 @@
 }
 |]
       , tcOutput =
-          [s|"ON": "ON"
-apiVersion: apps/v1
+          [s|apiVersion: apps/v1
+boolString: "true"
 expString: "1e3"
 isFalse: false
 isTrue: true
@@ -116,12 +115,11 @@
   The first line is followed by the
   second line
 multiLineWithSpaces: |2
-    This has
-  extra spaces at the beginning
+           This has extra
+       spaces at the beginning
 notMultiline: "This won't be\nmulti-lined"
 nullValue: null
 numberString: "12345"
-"off": "off"
 piString: "3.14"
 "quoted ! key": true
 spec: