diff --git a/requirements/ci/py36.yml b/requirements/ci/py36.yml
index f778704803..859b4fc18d 100644
--- a/requirements/ci/py36.yml
+++ b/requirements/ci/py36.yml
@@ -12,7 +12,7 @@ dependencies:
 
 # Core dependencies.
   - cartopy>=0.18
-  - cf-units>=2
+  - cf-units>=2.1.5
   - cftime<1.3.0
   - dask>=2
   - matplotlib
diff --git a/requirements/ci/py37.yml b/requirements/ci/py37.yml
index 5b21e9f778..dd7fb3b009 100644
--- a/requirements/ci/py37.yml
+++ b/requirements/ci/py37.yml
@@ -12,7 +12,7 @@ dependencies:
 
 # Core dependencies.
   - cartopy>=0.18
-  - cf-units>=2
+  - cf-units>=2.1.5
   - cftime<1.3.0
   - dask>=2
   - matplotlib
diff --git a/requirements/ci/py38.yml b/requirements/ci/py38.yml
index e09a7a7164..3d5009aee3 100644
--- a/requirements/ci/py38.yml
+++ b/requirements/ci/py38.yml
@@ -12,7 +12,7 @@ dependencies:
 
 # Core dependencies.
   - cartopy>=0.18
-  - cf-units>=2
+  - cf-units>=2.1.5
   - cftime<1.3.0
   - dask>=2
   - matplotlib
diff --git a/requirements/core.txt b/requirements/core.txt
index 9e0c4fb1bb..22c2165854 100644
--- a/requirements/core.txt
+++ b/requirements/core.txt
@@ -1,7 +1,7 @@
 # Core dependencies.
 
 cartopy>=0.18
-cf-units>=2
+cf-units>=2.1.5
 cftime<1.3.0
 dask[array]>=2
 matplotlib