diff --git a/bilby/core/sampler/ptemcee.py b/bilby/core/sampler/ptemcee.py
index 27aca317336ce54d7e372db144220f3faff6cb64..4fb90336f61fa9be483180c83421fd7048a4a8c9 100644
--- a/bilby/core/sampler/ptemcee.py
+++ b/bilby/core/sampler/ptemcee.py
@@ -793,7 +793,7 @@ def check_iteration(
                 "tau usable as {} < gradient_mean_log_posterior={}"
                 .format(gradient_mean_log_posterior, ci.gradient_mean_log_posterior)
             )
-            tau_usable = True
+            tau_usable *= True
         else:
             logger.debug(
                 "tau not usable as {} > gradient_mean_log_posterior={}"