diff --git a/bilby/core/sampler/dynesty.py b/bilby/core/sampler/dynesty.py
index ddd59ff084a0a9438d2e3a8201c2b2b757da5e67..f6c40ebf1ef6751b626736e3be3397a3fb64ea5c 100644
--- a/bilby/core/sampler/dynesty.py
+++ b/bilby/core/sampler/dynesty.py
@@ -121,6 +121,12 @@ class Dynesty(NestedSampler):
         signal.signal(signal.SIGINT, self.write_current_state_and_exit)
         signal.signal(signal.SIGALRM, self.write_current_state_and_exit)
 
+    def __getstate__(self):
+        """ For pickle: remove external_sampler, which can be an unpicklable "module" """
+        state = self.__dict__.copy()
+        del state['external_sampler']
+        return state
+
     @property
     def sampler_function_kwargs(self):
         keys = ['dlogz', 'print_progress', 'print_func', 'maxiter',