diff --git a/testing/mozharness/requirements.txt b/testing/mozharness/requirements.txt
index cc8569475537..aec0ff74cead 100644
--- a/testing/mozharness/requirements.txt
+++ b/testing/mozharness/requirements.txt
@@ -8,7 +8,7 @@ dulwich==0.8.7
 hg-git==0.4.0
 logilab-astng==0.24.2
 logilab-common==0.59.0
-mercurial==2.6.3
+mercurial==3.7.3
 mock==1.0.1
 nose==1.2.1
 ordereddict==1.1
@@ -22,4 +22,4 @@ virtualenv==1.5.1
 wsgiref==0.1.2
 urllib3==1.9.1
 google-api-python-client==1.3.1
-oauth2client==1.4.2
\ No newline at end of file
+oauth2client==1.4.2
diff --git a/testing/mozharness/tox.ini b/testing/mozharness/tox.ini
index c9ca51e05949..e2e1c3009e2d 100644
--- a/testing/mozharness/tox.ini
+++ b/testing/mozharness/tox.ini
@@ -1,5 +1,5 @@
 [tox]
-envlist = py27-hg2.6
+envlist = py27-hg3.7
 
 [base]
 deps =
@@ -15,15 +15,10 @@ setenv =
 commands =
     coverage run --source configs,mozharness,scripts --branch {envbindir}/nosetests -v --with-xunit --rednose --force-color {posargs}
 
-[testenv:py27-hg2.6]
+[testenv:py27-hg3.7]
 deps =
     {[base]deps}
-    mercurial==2.6.2
-
-[testenv:py27-hg3.2]
-deps =
-    {[base]deps}
-    mercurial==3.2.4
+    mercurial==3.7.3
 
 [testenv:py27-coveralls]
 deps=
diff --git a/testing/taskcluster/tasks/tests/mozharness-gecko.yml b/testing/taskcluster/tasks/tests/mozharness-gecko.yml
index 6fd7dc43cdcc..5fd8b11c1cc6 100644
--- a/testing/taskcluster/tasks/tests/mozharness-gecko.yml
+++ b/testing/taskcluster/tasks/tests/mozharness-gecko.yml
@@ -30,7 +30,7 @@ task:
           tc-vcs checkout ./gecko {{base_repository}} {{head_repository}} {{head_rev}} {{head_ref}} &&
           cd gecko/testing/mozharness &&
           pip install tox &&
-          tox -e py27-hg2.6 -e py27-hg3.2
+          tox -e py27-hg3.7
   extra:
     extra:
         build_product: '{{build_product}}'