gistfile.patch

diff --git a/index.js b/index.js
index b2a25ee..b34ae25 100644
--- a/index.js
+++ b/index.js
@@ -21,19 +21,14 @@ const resolveFrom = require('resolve-from')
 const DEFAULT_NODE_GYP_PATH = resolveFrom(__dirname, 'node-gyp/bin/node-gyp')
 const hookStatCache = new Map()
 
-let PATH = 'PATH'
+let PATH = isWindows ? 'Path' : 'PATH'
 
 // windows calls its path 'Path' usually, but this is not guaranteed.
-if (isWindows) {
-  PATH = 'Path'
-  if (!process.env[PATH]) {
-    Object.keys(process.env).forEach(function (e) {
-      if (e.match(/^PATH$/i)) {
-        PATH = e
-      }
-    })
-  }
-}
+// merge them all together in the order they appear in the object.
+const mergePath = env =>
+  Object.keys(env).filter(p => /^path$/i.test(p) && env[p])
+    .map(p => env[p])
+    .join(';')
 
 exports._pathEnvName = PATH
 
@@ -127,7 +122,8 @@ function lifecycle_ (pkg, stage, wd, opts, env, cb) {
     pathArr.push(path.dirname(process.execPath))
   }
 
-  if (env[PATH]) pathArr.push(env[PATH])
+  const envPath = mergePath(env)
+  if (envPath) pathArr.push(envPath)
   env[PATH] = pathArr.join(isWindows ? ';' : ':')
 
   var packageLifecycle = pkg.scripts && pkg.scripts.hasOwnProperty(stage)