diff --git bp-members/bp-members-signup.php bp-members/bp-members-signup.php
index 89b28b9..adbefb8 100644
--- bp-members/bp-members-signup.php
+++ bp-members/bp-members-signup.php
@@ -308,7 +308,7 @@ function bp_core_validate_user_signup( $user_name, $user_email ) {
 		$errors->add( 'user_name', __( 'Please enter a username', 'buddypress' ) );
 
 	$maybe = array();
-	preg_match( "/[a-z0-9]+/", $user_name, $maybe );
+	preg_match( "/[a-zA-Z0-9]+/", $user_name, $maybe );
 
 	// Make sure illegal names include BuddyPress slugs and values
 	bp_core_flush_illegal_names();