diff --git a/chrombpnet/helpers/make_gc_matched_negatives/get_genomewide_gc_buckets/get_genomewide_gc_bins.py b/chrombpnet/helpers/make_gc_matched_negatives/get_genomewide_gc_buckets/get_genomewide_gc_bins.py
index 8eea53c2..b8d51f3f 100644
--- a/chrombpnet/helpers/make_gc_matched_negatives/get_genomewide_gc_buckets/get_genomewide_gc_bins.py
+++ b/chrombpnet/helpers/make_gc_matched_negatives/get_genomewide_gc_buckets/get_genomewide_gc_bins.py
@@ -27,7 +27,7 @@ def get_genomewide_gc(genome_fa, outf, width, stride):
     3000-4000 and delete 1000-2000. And repeat.
     """
 
-    f = pyfaidx.Fasta(genome_fa, as_raw=True)
+    f = pyfaidx.Fasta(genome_fa, as_raw=True, rebuild=False)
     outf = open(outf, 'w')
 
     div = width//stride