diff --git a/sampler_requirements.txt b/sampler_requirements.txt
index 3204ab305f260dfdb7e507e564db31b17c12e959..ee82c447b494093f00031f66b7ffd9515b569664 100644
--- a/sampler_requirements.txt
+++ b/sampler_requirements.txt
@@ -3,5 +3,6 @@ dynesty
 emcee
 nestle
 ptemcee
-pymc3>=3.6
+pymc3==3.6; python_version <= '2.7'
+pymc3>=3.6; python_version > '3.4'
 pymultinest
\ No newline at end of file