diff --git a/sparsecoding/priors/spike_slab.py b/sparsecoding/priors/spike_slab.py
index e6c6ccb..6336cf0 100644
--- a/sparsecoding/priors/spike_slab.py
+++ b/sparsecoding/priors/spike_slab.py
@@ -91,7 +91,7 @@ def log_prob(
         log_prob[slab_mask] = (
             torch.log(torch.tensor(1. - self.p_spike))
             - torch.log(torch.tensor(self.scale))
-            - sample[slab_mask] / self.scale
+            - torch.abs(sample[slab_mask]) / self.scale
         )
         if self.positive_only:
             log_prob[sample < 0.] = -torch.inf