diff --git a/rsa/model_rdm.py b/rsa/model_rdm.py
index 4050dbe..456131e 100755
--- a/rsa/model_rdm.py
+++ b/rsa/model_rdm.py
@@ -41,8 +41,7 @@ def dissimilarity(self, fp_row, fp_col, idx):
     def apply(self, processes=1, chunksize=10, do_disable_tqdm=False):
 
         triu_rows, triu_cols = self.get_triu_rows_cols()
-        if self.model_rdm_triu is None:
-            self.model_rdm_triu = np.zeros((triu_rows.size,)) + ENTRY_EMPTY
+        self._init_model_rdm_triu()
 
         with mp.get_context("spawn").Pool(processes=processes) as pool:
             result = pool.starmap(self.dissimilarity,