Index: wp-includes/pluggable.php
===================================================================
--- wp-includes/pluggable.php	(revision 19601)
+++ wp-includes/pluggable.php	(working copy)
@@ -1628,8 +1628,11 @@
 			$default = $avatar_default;
 	}
 
-	if ( !empty($email) )
+	if ( !empty($email) ) {
+		if( false !== strpos( $email, ' ' ) )
+			$email = str_replace( ' ', '', $email );
 		$email_hash = md5( strtolower( $email ) );
+	}
 
 	if ( is_ssl() ) {
 		$host = 'https://secure.gravatar.com';