diff --git a/src/calibre/gui2/convert/regex_builder.py b/src/calibre/gui2/convert/regex_builder.py
index b1d8fbcbd5..83e548f81d 100644
--- a/src/calibre/gui2/convert/regex_builder.py
+++ b/src/calibre/gui2/convert/regex_builder.py
@@ -25,7 +25,7 @@ class RegexHighlighter(QSyntaxHighlighter):
         self.regex = u''
 
     def update_regex(self, regex):
-        self.regex = qstring_to_unicode(regex)
+        self.regex = regex
         self.rehighlight()
 
     def highlightBlock(self, text):
@@ -59,14 +59,22 @@ class RegexBuilder(QDialog, Ui_RegexBuilder):
             self.select_format(db, book_id)
 
         self.connect(self.button_box, SIGNAL('clicked(QAbstractButton*)'), self.button_clicked)
-        self.connect(self.regex, SIGNAL('textChanged(QString)'), self.highlighter.update_regex)
-        self.connect(self.highlighter, SIGNAL('regex_valid(PyQt_PyObject)'), self.regex_valid)
+        self.connect(self.regex, SIGNAL('textChanged(QString)'), self.regex_valid)
+        self.connect(self.test, SIGNAL('clicked()'), self.do_test)
 
     def regex_valid(self, valid):
-        if valid:
-            self.regex.setStyleSheet('QLineEdit { color: black; background-color: white; }')
+        regex = qstring_to_unicode(self.regex.text())
+        if regex:
+            try:
+                re.compile(regex)
+                self.regex.setStyleSheet('QLineEdit { color: black; background-color: rgba(0,255,0,20%); }')
+            except:
+                self.regex.setStyleSheet('QLineEdit { color: black; background-color: rgb(255,0,0,20%); }')
         else:
-            self.regex.setStyleSheet('QLineEdit { color: black; background-color: rgb(255,0,0,20%); }')
+            self.regex.setStyleSheet('QLineEdit { color: black; background-color: white; }')
+
+    def do_test(self):
+        self.highlighter.update_regex(qstring_to_unicode(self.regex.text()))
 
     def select_format(self, db, book_id):
         format = None
diff --git a/src/calibre/gui2/convert/regex_builder.ui b/src/calibre/gui2/convert/regex_builder.ui
index 3448c4dded..af17917676 100644
--- a/src/calibre/gui2/convert/regex_builder.ui
+++ b/src/calibre/gui2/convert/regex_builder.ui
@@ -14,7 +14,7 @@
    <string>Regex Builder</string>
   </property>
   <layout class="QGridLayout" name="gridLayout">
-   <item row="1" column="0" colspan="2">
+   <item row="1" column="0" colspan="5">
     <widget class="QGroupBox" name="groupBox">
      <property name="title">
       <string>Preview</string>
@@ -36,7 +36,7 @@
      </layout>
     </widget>
    </item>
-   <item row="2" column="1">
+   <item row="2" column="4">
     <widget class="QDialogButtonBox" name="button_box">
      <property name="orientation">
       <enum>Qt::Horizontal</enum>
@@ -53,8 +53,19 @@
      </property>
     </widget>
    </item>
-   <item row="0" column="1">
-    <widget class="QLineEdit" name="regex"/>
+   <item row="0" column="1" colspan="4">
+    <layout class="QHBoxLayout" name="horizontalLayout">
+     <item>
+      <widget class="QLineEdit" name="regex"/>
+     </item>
+     <item>
+      <widget class="QPushButton" name="test">
+       <property name="text">
+        <string>Test</string>
+       </property>
+      </widget>
+     </item>
+    </layout>
    </item>
   </layout>
  </widget>