diff --git a/lib/ace/mode/ruby_highlight_rules.js b/lib/ace/mode/ruby_highlight_rules.js
index 8de4d903..0d0cabac 100644
--- a/lib/ace/mode/ruby_highlight_rules.js
+++ b/lib/ace/mode/ruby_highlight_rules.js
@@ -128,7 +128,7 @@ var RubyHighlightRules = function() {
                 regex : "[:](?:[A-Za-z_]|[@$](?=[a-zA-Z0-9_]))[a-zA-Z0-9_]*[!=?]?"
 	       }, {
 	            token : "constant.numeric", // hex
-	            regex : "0[xX][0-9a-fA-F]+\\b"
+	            regex : "0[xX][0-9a-fA-F](?:[0-9a-fA-F]|_(?=[0-9a-fA-F]))*\\b"
 	        }, {
 	            token : "constant.numeric", // float
 	            regex : "[+-]?\\d(?:\\d|_(?=\\d))*(?:(?:\\.\\d(?:\\d|_(?=\\d))*)?(?:[eE][+-]?\\d+)?)?\\b"
diff --git a/lib/ace/mode/ruby_tokenizer_test.js b/lib/ace/mode/ruby_tokenizer_test.js
index 37f4e2a3..f8dd7eb8 100644
--- a/lib/ace/mode/ruby_tokenizer_test.js
+++ b/lib/ace/mode/ruby_tokenizer_test.js
@@ -61,6 +61,13 @@ module.exports = {
             ":th!ing", ":thing#"]);
     },
 
+    "test: hex tokenizer" : function() {
+        assertValidTokens(this.tokenizer, "constant.numeric",
+            ["0x9a", "0XA1", "0x9_a"]);
+        assertInvalidTokens(this.tokenizer, "constant.numeric",
+            ["0x", "0x_9a", "0x9a_"]);
+    },
+
     "test: float tokenizer" : function() {
         assertValidTokens(this.tokenizer, "constant.numeric",
             ["1", "+1", "-1", "12_345", "0.000_1"]);