diff --git a/zanata-war/src/main/java/org/zanata/action/RegisterAction.java b/zanata-war/src/main/java/org/zanata/action/RegisterAction.java
index 71871279b0..bb6d836d0f 100644
--- a/zanata-war/src/main/java/org/zanata/action/RegisterAction.java
+++ b/zanata-war/src/main/java/org/zanata/action/RegisterAction.java
@@ -99,7 +99,7 @@ public void setUsername(String username)
 
    @NotEmpty
    @Size(min = 3, max = 20)
-   @Pattern(regexp = "^[a-z\\d_]{3,20}$")
+   @Pattern(regexp = "^[a-z\\d_]{3,20}$", message = "{validation.username.constraints}")
    public String getUsername()
    {
       return username;
diff --git a/zanata-war/src/main/resources/ValidationMessages.properties b/zanata-war/src/main/resources/ValidationMessages.properties
index 5fe48b4ad2..cfdeb5f469 100644
--- a/zanata-war/src/main/resources/ValidationMessages.properties
+++ b/zanata-war/src/main/resources/ValidationMessages.properties
@@ -15,4 +15,6 @@ javax.validation.constraints.Url.message=must be a valid URL
 #javax.validation.constraints.UrlNoSlash.message=must be a valid URL (without final slash)
 javax.validation.constraints.NotDuplicateEmail.message=duplicate email
 javax.validation.constraints.EmailList.message=invalid email or incorrect comma placement
-org.jboss.seam.captcha.error=incorrect response
\ No newline at end of file
+org.jboss.seam.captcha.error=incorrect response
+
+validation.username.constraints=lowercase letters and digits (regex "{regexp}")
\ No newline at end of file