diff --git a/src/main/python/org/broadinstitute/hellbender/gcnvkernel/models/model_ploidy.py b/src/main/python/org/broadinstitute/hellbender/gcnvkernel/models/model_ploidy.py
index 2723bdf6a7c..03cef313683 100644
--- a/src/main/python/org/broadinstitute/hellbender/gcnvkernel/models/model_ploidy.py
+++ b/src/main/python/org/broadinstitute/hellbender/gcnvkernel/models/model_ploidy.py
@@ -229,7 +229,7 @@ def __init__(self,
 
         # sample-specific contig unexplained variance
         psi_s = Exponential(name='psi_s',
-                            lam=1.0 / ploidy_config.psi_j_scale,
+                            lam=1.0 / ploidy_config.psi_s_scale,
                             shape=(ploidy_workspace.num_samples,))
         register_as_sample_specific(psi_s, sample_axis=0)