diff --git a/src/main/java/tk/draganczuk/url/Utils.java b/src/main/java/tk/draganczuk/url/Utils.java
index 9292067..174a7b5 100644
--- a/src/main/java/tk/draganczuk/url/Utils.java
+++ b/src/main/java/tk/draganczuk/url/Utils.java
@@ -6,7 +6,7 @@ import java.util.regex.Pattern;
 public class Utils {
 	private static final Random random = new Random(System.currentTimeMillis());
 
-	private static final String SHORT_URL_PATTERN = "[a-z0-9]+";
+	private static final String SHORT_URL_PATTERN = "[a-z0-9_-]+";
 	private static final Pattern PATTERN = Pattern.compile(SHORT_URL_PATTERN);
 
 	public static String randomString() {
diff --git a/src/main/resources/public/index.html b/src/main/resources/public/index.html
index e53d4fe..897ebb3 100644
--- a/src/main/resources/public/index.html
+++ b/src/main/resources/public/index.html
@@ -33,9 +33,10 @@
                 <input type="url" name="longUrl" id="longUrl" placeholder="Long URL" required/>
             </div>
             <div class="pure-control-group">
-                <label for="shortUrl">Short URL (Optional)</label>
+                <label for="shortUrl">Short URL (Optional). Only letters, number dashes and underscores
+                    permitted</label>
                 <input type="text" name="shortUrl" id="shortUrl" placeholder="Short URL (optional)"
-                       pattern="[a-z0-9]+"/>
+                       pattern="[a-z0-9_-]+"/>
             </div>
             <div class="pure-controls">
                 <button class="pure-button pure-button-primary">Submit</button>