diff --git a/env_os.go b/env_os.go
index a6a014a..eba07a6 100644
--- a/env_os.go
+++ b/env_os.go
@@ -1,4 +1,4 @@
-// +build appengine
+// +build appengine go1.5
 
 package envconfig
 
diff --git a/env_syscall.go b/env_syscall.go
index 9d98085..4254540 100644
--- a/env_syscall.go
+++ b/env_syscall.go
@@ -1,4 +1,4 @@
-// +build !appengine
+// +build !appengine,!go1.5
 
 package envconfig