diff --git a/credentials/credentials_util_go19.go b/credentials/credentials_util_go19.go
index 615578a4..b006e9bc 100644
--- a/credentials/credentials_util_go19.go
+++ b/credentials/credentials_util_go19.go
@@ -1,4 +1,4 @@
-// +build go1.9
+// +build go1.9,!appengine
 
 /*
  *
diff --git a/credentials/credentials_util_pre_go19.go b/credentials/credentials_util_pre_go19.go
index 9466e195..5e65bb2c 100644
--- a/credentials/credentials_util_pre_go19.go
+++ b/credentials/credentials_util_pre_go19.go
@@ -1,4 +1,4 @@
-// +build !go1.9
+// +build !go1.9 appengine
 
 /*
  *