diff --git a/generate_theoric_random_graph.py b/generate_theoric_random_graph.py
index 2f6f54130391ccbc114ef02076a3d734976a25cf..c9d9425c8230acbcbe28d827222fb04a3ab2c645 100644
--- a/generate_theoric_random_graph.py
+++ b/generate_theoric_random_graph.py
@@ -27,7 +27,7 @@ def generate_sbm_prob_matrix(nb_of_blocks,prob_btw_block=0.1):
 
 GRAPH_SIZE = [50,75,100]
 OUTPUT_DIR = args.output_dir
-if os.path.exists(OUTPUT_DIR):
+if not os.path.exists(OUTPUT_DIR):
     raise FileExistsError("Output directory does not exists !")
 
 parameters = {