diff --git a/roles/fetch-tox-output/README.rst b/roles/fetch-tox-output/README.rst
index a20fb1f4d..27d08ee2a 100644
--- a/roles/fetch-tox-output/README.rst
+++ b/roles/fetch-tox-output/README.rst
@@ -5,7 +5,9 @@ Collect log output from a tox build
 .. zuul:rolevar:: tox_envlist
    :default: venv
 
-   Which tox environment to fetch log output from.
+    Comma separated string with test environmens to fetch log output from.
+    ``ALL`` fetches all environments while an empty string fetches all test
+    environments configured with ``envlist`` in tox.
 
 .. zuul:rolevar:: tox_executable
    :default: tox
diff --git a/roles/fetch-tox-output/tasks/main.yaml b/roles/fetch-tox-output/tasks/main.yaml
index 93dc96662..9d58a7c51 100644
--- a/roles/fetch-tox-output/tasks/main.yaml
+++ b/roles/fetch-tox-output/tasks/main.yaml
@@ -23,26 +23,31 @@
 - name: Set envlist fact
   set_fact:
     envlist: "{{ tox_envlist.split(',') }}"
-  when: tox_envlist is defined
+  when: tox_envlist is defined and tox_envlist != 'ALL' and tox_envlist
 
 - name: Find all default environments
   command: "{{ tox_executable }} -l"
   args:
     chdir: "{{ zuul_work_dir }}"
   register: tox_environments
-  when: tox_envlist is not defined
+  when: tox_envlist is not defined or
+        not tox_envlist
 
 - name: Find all default environments
   command: "{{ tox_executable }} -a"
   args:
     chdir: "{{ zuul_work_dir }}"
   register: tox_environments
-  when: tox_envlist == 'ALL'
+  when:
+    - tox_envlist is defined
+    - tox_envlist == 'ALL'
 
 - name: Set envlist fact
   set_fact:
     envlist: "{{ tox_environments.stdout_lines }}"
-  when: tox_envlist is not defined or tox_envlist == 'ALL'
+  when: tox_envlist is not defined or
+        not tox_envlist or
+        tox_envlist == 'ALL'
 
 - name: Copy tox logs
   copy:
diff --git a/roles/tox/README.rst b/roles/tox/README.rst
index e770a3507..89cb3a499 100644
--- a/roles/tox/README.rst
+++ b/roles/tox/README.rst
@@ -9,7 +9,9 @@ Runs tox for a project
 .. zuul:rolevar:: tox_envlist
    :default: venv
 
-   Which tox environment to run.
+   Comma separated string with test environments tox should run.
+   ``ALL`` runs all test environments while an empty string runs
+   all test environments configured with ``envlist`` in tox.
 
 .. zuul:rolevar:: tox_executable
    :default: tox
diff --git a/roles/tox/tasks/main.yaml b/roles/tox/tasks/main.yaml
index c498d8f11..9af1068f7 100644
--- a/roles/tox/tasks/main.yaml
+++ b/roles/tox/tasks/main.yaml
@@ -31,13 +31,23 @@
 
 - name: Emit tox command
   debug:
-    msg: "Running tox: {{ tox_executable }} -e{{ tox_envlist }} {{ tox_extra_args }}"
+    msg: >-
+      {{ tox_executable }}
+      {% if tox_envlist is defined and tox_envlist %}
+      -e{{ tox_envlist }}
+      {% endif %}
+      {{ tox_extra_args }}
 
 - name: Run tox
   args:
     chdir: "{{ zuul_work_dir }}"
   environment: "{{ tox_environment|combine(tox_constraints_env|default({})) }}"
-  command: "{{ tox_executable }} -e{{ tox_envlist }} {{ tox_extra_args }}"
+  command: >-
+    {{ tox_executable }}
+    {% if tox_envlist is defined and tox_envlist %}
+    -e{{ tox_envlist }}
+    {% endif %}
+    {{ tox_extra_args }}
   # Note: This intentionally ignores errors to give us the chance to look
   # for file comments in the stdout. In case of an error this will be returned
   # in a later task.