diff --git a/roles/tox/README.rst b/roles/tox/README.rst
index 45fa89abf..45f8a3daa 100644
--- a/roles/tox/README.rst
+++ b/roles/tox/README.rst
@@ -6,12 +6,6 @@ Runs tox for a project
 
    Environment variables to pass in to the tox run.
 
-.. zuul:rolevar:: tox_environment_defaults
-
-   Default environment variables to pass in to the tox run. Intended
-   to allow setting a set of environment variables in a base job but
-   to still allow specific settings on a per-job or per-variant basis.
-
 .. zuul:rolevar:: tox_envlist
    :default: venv
 
@@ -27,7 +21,12 @@ Runs tox for a project
 
    String of extra command line options to pass to tox.
 
+.. zuul:rolevar:: tox_upper_constraints_file
+
+   Path to an upper constraints file. Will be provided to tox via
+   UPPER_CONSTRAINTS_FILE environment variable if it exists.
+
 .. zuul:rolevar:: zuul_work_dir
-   :default: src/{{ zuul.project.canonical_name }}
+   :default: {{ zuul.project.src_dir }}
 
    Directory to run tox in.
diff --git a/roles/tox/defaults/main.yaml b/roles/tox/defaults/main.yaml
index cb70ca0a2..f4b08abd2 100644
--- a/roles/tox/defaults/main.yaml
+++ b/roles/tox/defaults/main.yaml
@@ -1,8 +1,7 @@
 ---
 tox_environment: {}
-tox_environment_defaults: {}
 tox_envlist: venv
 tox_executable: tox
 tox_extra_args: -vv
 
-zuul_work_dir: "src/{{ zuul.project.canonical_name }}"
+zuul_work_dir: "{{ zuul.project.src_dir }}"
diff --git a/roles/tox/tasks/main.yaml b/roles/tox/tasks/main.yaml
index 44f7ed797..edb8acc4a 100644
--- a/roles/tox/tasks/main.yaml
+++ b/roles/tox/tasks/main.yaml
@@ -1,14 +1,25 @@
-- name: Require tox_envlist variable - {{ tox_envlist }}
+- name: Require tox_envlist variable
   fail:
-    msg: "tox_envlist is required for this role"
+    msg: tox_envlist is required for this role
   when: tox_envlist is not defined
 
-- name: Create my_tox_environment variable
+- name: Check to see if the constraints file exists
+  stat:
+    path: "{{ tox_upper_constraints_file }}"
+    get_checksum: false
+    get_mime: false
+    get_md5: false
+  register: stat_results
+  when: tox_upper_constraints_file is defined
+
+- name: Record file location
   set_fact:
-    my_tox_environment: "{{ tox_environment_defaults | combine(tox_environment) }}"
+    tox_upper_constraints_env:
+      UPPER_CONSTRAINTS_FILE: "{{ tox_upper_constraints_file }}"
+  when: not stat_results|skipped and stat_results.stat.exists
 
 - name: Run tox
   args:
-    chdir: "{{ zuul_work_dir | default(omit) }}"
-  environment: "{{ my_tox_environment }}"
+    chdir: "{{ zuul_work_dir }}"
+  environment: "{{ tox_environment|combine(tox_upper_constraints_env|default({})) }}"
   command: "{{ tox_executable }} -e{{ tox_envlist }} {{ tox_extra_args }}"
diff --git a/zuul.yaml b/zuul.yaml
index edbfc0ecb..fbea82b7c 100644
--- a/zuul.yaml
+++ b/zuul.yaml
@@ -34,11 +34,16 @@
       .. zuul:jobvar:: tox_extra_args
 
          String containing extra arguments to append to the tox command line.
+
+      .. zuul:jobvar: tox_upper_constraints_file
+
+         Path to an upper constraints file. Will be provided to tox via
+         UPPER_CONSTRAINTS_FILE environment variable if it exists.
     run: playbooks/tox/run
     pre-run: playbooks/tox/pre
     post-run: playbooks/tox/post
     vars:
-      tox_environment_defaults:
+      tox_environment:
         NOSE_WITH_HTML_OUTPUT: 1
         NOSE_HTML_OUT_FILE: nose_results.html
         NOSE_WITH_XUNIT: 1