diff --git a/code/Clustering.pl b/code/Clustering.pl
index 988c4504881c21925acd00a97fd2f9390b0fd2e6..572c8f62194e78c4bdb59e523de6aa560a295166 100755
--- a/code/Clustering.pl
+++ b/code/Clustering.pl
@@ -27,7 +27,7 @@ USAGE
 
 my $ID_file = "seg.id";  #segment IDs inside cluster
 my $linkage_file = "seg.link";
-my $cluster_dir "cluster_"; #prefix of directory names
+my $cluster_dir = "cluster_"; #prefix of directory names
 
 my %opts;
 GetOptions(\%opts , "s=i" , "i=s", "m=i", "link=s", "bk=s", "seq=s", "h");