diff --git a/requirements.in b/requirements.in
index adba86d..8cd3b11 100644
--- a/requirements.in
+++ b/requirements.in
@@ -4,3 +4,4 @@ nbgitpuller
 pymc3
 graphviz
 seaborn
+numpy==1.21.5
diff --git a/requirements.txt b/requirements.txt
index 73bf38d..988409a 100644
--- a/requirements.txt
+++ b/requirements.txt
@@ -123,8 +123,9 @@ netcdf4==1.5.8
     # via arviz
 notebook==6.4.6
     # via nbgitpuller
-numpy==1.22.0
+numpy==1.21.5
     # via
+    #   -r requirements.in
     #   arviz
     #   cftime
     #   fastprogress