diff --git a/lib/config/core.js b/lib/config/core.js
index b9851f98d0e0c..1beca6a509436 100644
--- a/lib/config/core.js
+++ b/lib/config/core.js
@@ -411,11 +411,23 @@ function envReplace (f) {
   return f.replace(envExpr, function (orig, esc, name) {
     esc = esc.length && esc.length % 2
     if (esc) return orig
-    if (undefined === process.env[name]) {
-      throw new Error('Failed to replace env in config: ' + orig)
+    var failbackExpr = /(\\*)-/g
+    var failbackMatch
+    var failback
+    while ((failbackMatch = failbackExpr.exec(name))) {
+      esc = failbackMatch[1]
+      esc = esc.length && esc.length % 2
+      if (esc) continue
+      failback = name.slice(failbackMatch.index + 1)
+      name = name.slice(0, failbackMatch.index)
+      break
     }
-
-    return process.env[name]
+    if (undefined !== process.env[name]) {
+      return process.env[name]
+    } else if (failbackMatch) {
+      return failback
+    }
+    throw new Error('Failed to replace env in config: ' + orig)
   })
 }