diff --git a/js/os.ts b/js/os.ts
index 30c9743488..a692eeb1a8 100644
--- a/js/os.ts
+++ b/js/os.ts
@@ -81,12 +81,11 @@ export function codeCache(
   assert(baseRes == null); // Expect null or error.
 }
 
-function createEnv(_inner: msg.EnvironRes): { [index: string]: string } {
+function createEnv(inner: msg.EnvironRes): { [index: string]: string } {
   const env: { [index: string]: string } = {};
 
-  for (let i = 0; i < _inner.mapLength(); i++) {
-    const item = _inner.map(i)!;
-
+  for (let i = 0; i < inner.mapLength(); i++) {
+    const item = inner.map(i)!;
     env[item.key()!] = item.value()!;
   }
 
diff --git a/src/main.rs b/src/main.rs
index 0defa68385..b7efd40afa 100644
--- a/src/main.rs
+++ b/src/main.rs
@@ -31,6 +31,7 @@ mod http_util;
 pub mod isolate;
 pub mod libdeno;
 pub mod msg;
+pub mod msg_util;
 pub mod ops;
 pub mod permissions;
 pub mod resources;
diff --git a/src/msg.fbs b/src/msg.fbs
index f402960a10..5f86ad56a8 100644
--- a/src/msg.fbs
+++ b/src/msg.fbs
@@ -182,10 +182,10 @@ table SetEnv {
 }
 
 table EnvironRes {
-  map: [EnvPair];
+  map: [KeyValue];
 }
 
-table EnvPair {
+table KeyValue {
   key: string;
   value: string;
 }
diff --git a/src/msg_util.rs b/src/msg_util.rs
new file mode 100644
index 0000000000..350e8ac10a
--- /dev/null
+++ b/src/msg_util.rs
@@ -0,0 +1,21 @@
+// Copyright 2018 the Deno authors. All rights reserved. MIT license.
+// Helpers for serialization.
+use flatbuffers;
+use msg;
+
+pub fn serialize_key_value<'bldr>(
+  builder: &mut flatbuffers::FlatBufferBuilder<'bldr>,
+  key: &str,
+  value: &str,
+) -> flatbuffers::WIPOffset<msg::KeyValue<'bldr>> {
+  let key = builder.create_string(&key);
+  let value = builder.create_string(&value);
+  msg::KeyValue::create(
+    builder,
+    &msg::KeyValueArgs {
+      key: Some(key),
+      value: Some(value),
+      ..Default::default()
+    },
+  )
+}
diff --git a/src/ops.rs b/src/ops.rs
index e93ec5cf72..9bca698ba2 100644
--- a/src/ops.rs
+++ b/src/ops.rs
@@ -8,6 +8,7 @@ use isolate::Isolate;
 use isolate::IsolateState;
 use isolate::Op;
 use msg;
+use msg_util;
 use resources;
 use resources::Resource;
 use version;
@@ -358,19 +359,8 @@ fn op_env(
 
   let builder = &mut FlatBufferBuilder::new();
   let vars: Vec<_> = std::env::vars()
-    .map(|(key, value)| {
-      let key = builder.create_string(&key);
-      let value = builder.create_string(&value);
-
-      msg::EnvPair::create(
-        builder,
-        &msg::EnvPairArgs {
-          key: Some(key),
-          value: Some(value),
-          ..Default::default()
-        },
-      )
-    }).collect();
+    .map(|(key, value)| msg_util::serialize_key_value(builder, &key, &value))
+    .collect();
   let tables = builder.create_vector(&vars);
   let inner = msg::EnvironRes::create(
     builder,