diff --git a/requirements/tests.txt b/requirements/tests.txt
index 3ecc996..62aa1bd 100644
--- a/requirements/tests.txt
+++ b/requirements/tests.txt
@@ -1,5 +1,5 @@
 # latest version to validate behavior on pure python env
-pytest
-pytest-xdist  # for --boxed
-hypothesis
-numpy
+pytest==4.0.2
+pytest-xdist==1.25.0  # for --boxed
+hypothesis==3.84.5
+numpy==1.15.4