diff --git a/roles/tox/README.rst b/roles/tox/README.rst
index 40932402b..215c3ff97 100644
--- a/roles/tox/README.rst
+++ b/roles/tox/README.rst
@@ -24,7 +24,8 @@ Runs tox for a project
 .. zuul:rolevar:: tox_constraints_file
 
    Path to a pip constraints file. Will be provided to tox via
-   UPPER_CONSTRAINTS_FILE environment variable if it exists.
+   TOX_CONSTRAINTS_FILE (deprecated but currently still supported
+   name is UPPER_CONSTRAINTS_FILE) environment variable if it exists.
 
 .. zuul:rolevar:: tox_install_siblings
    :default: true
diff --git a/roles/tox/tasks/main.yaml b/roles/tox/tasks/main.yaml
index b1f464fb8..ea828f033 100644
--- a/roles/tox/tasks/main.yaml
+++ b/roles/tox/tasks/main.yaml
@@ -20,6 +20,8 @@
 - name: Record file location
   set_fact:
     tox_constraints_env:
+      TOX_CONSTRAINTS_FILE: "{{ tox_constraints_file }}"
+      # Backward compatibility, to be removed
       UPPER_CONSTRAINTS_FILE: "{{ tox_constraints_file }}"
   when: tox_constraints_file is defined
 
diff --git a/zuul.yaml b/zuul.yaml
index 11ce741cd..a6d3ae237 100644
--- a/zuul.yaml
+++ b/zuul.yaml
@@ -110,7 +110,7 @@
       .. zuul:jobvar: tox_constraints_file
 
          Path to a pip constraints file. Will be provided to tox in the
-         UPPER_CONSTRAINTS_FILE environment variable if it exists.
+         TOX_CONSTRAINTS_FILE environment variable if it exists.
 
       .. zuul:jobvar: tox_install_siblings
          :default: true
@@ -269,7 +269,7 @@
       .. zuul:jobvar: tox_constraints_file
 
          Path to a pip constraints file. Will be provided to tox in the
-         UPPER_CONSTRAINTS_FILE environment variable if it exists.
+         TOX_CONSTRAINTS_FILE environment variable if it exists.
 
       .. zuul:jobvar: tox_install_siblings
          :default: true