diff --git a/lib/utils/git.js b/lib/utils/git.js
index 6770853dd9622..1951640e81568 100644
--- a/lib/utils/git.js
+++ b/lib/utils/git.js
@@ -28,6 +28,16 @@ function execGit (args, options, cb) {
 
 function spawnGit (args, options) {
   log.info('git', args)
+  // If we're already in a git command (eg, running test as an exec
+  // line in an interactive rebase) then these environment variables
+  // will force git to operate on the current project, instead of
+  // checking out/fetching/etc. whatever the user actually intends.
+  options.env = options.env || Object.keys(process.env)
+    .filter(k => !/^GIT/.test(k))
+    .reduce((set, k) => {
+      set[k] = process.env[k]
+      return set
+    }, {})
   return spawn(git, prefixGitArgs().concat(args || []), options)
 }
 
diff --git a/test/common-tap.js b/test/common-tap.js
index d54a869995451..e15d5dab2487d 100644
--- a/test/common-tap.js
+++ b/test/common-tap.js
@@ -7,6 +7,12 @@ var readCmdShim = require('read-cmd-shim')
 var isWindows = require('../lib/utils/is-windows.js')
 var Bluebird = require('bluebird')
 
+// remove any git envs so that we don't mess with the main repo
+// when running git subprocesses in tests
+Object.keys(process.env).filter(k => /^GIT/.test(k)).forEach(
+  k => delete process.env[k]
+)
+
 // cheesy hackaround for test deps (read: nock) that rely on setImmediate
 if (!global.setImmediate || !require('timers').setImmediate) {
   require('timers').setImmediate = global.setImmediate = function () {