diff --git a/src/css/Properties.js b/src/css/Properties.js
index 4a9beeea..1acc7d3d 100644
--- a/src/css/Properties.js
+++ b/src/css/Properties.js
@@ -16,7 +16,7 @@ var Properties = module.exports = {
     "alignment-baseline"            : "auto | baseline | use-script | before-edge | text-before-edge | after-edge | text-after-edge | central | middle | ideographic | alphabetic | hanging | mathematical",
     "animation"                     : 1,
     "animation-delay"               : "<time>#",
-    "animation-direction"           : "[ normal | alternate ]#",
+    "animation-direction"           : "<single-animation-direction>#",
     "animation-duration"            : "<time>#",
     "animation-fill-mode"           : "[ none | forwards | backwards | both ]#",
     "animation-iteration-count"     : "[ <number> | infinite ]#",
diff --git a/src/css/ValidationTypes.js b/src/css/ValidationTypes.js
index 468fe856..78390ba1 100644
--- a/src/css/ValidationTypes.js
+++ b/src/css/ValidationTypes.js
@@ -282,6 +282,9 @@ copy(ValidationTypes, {
 
         "<shape-box>": "<box> | margin-box",
 
+        "<single-animation-direction>":
+            "normal | reverse | alternate | alternate-reverse",
+
         "<single-animation-name>": function(part) {
             return this["<ident>"](part) &&
                 /^-?[a-z_][-a-z0-9_]+$/i.test(part) &&
diff --git a/tests/css/Validation.js b/tests/css/Validation.js
index 3024a123..2a8e627f 100644
--- a/tests/css/Validation.js
+++ b/tests/css/Validation.js
@@ -83,6 +83,22 @@ var YUITest = require("yuitest"),
 
     var suite = new YUITest.TestSuite("Validation Tests");
 
+    suite.add(new ValidationTestCase({
+        property: "animation-direction",
+
+        valid: [
+            "normal",
+            "reverse",
+            "alternate",
+            "alternate-reverse",
+            "alternate, reverse, normal",
+        ],
+
+        invalid: {
+            "1px" : "Expected (<single-animation-direction>#) but found '1px'."
+        }
+    }));
+
     suite.add(new ValidationTestCase({
         property: "animation-fill-mode",