diff --git a/packages/metro-bundler/src/JSTransformer/worker/index.js b/packages/metro-bundler/src/JSTransformer/worker/index.js
index 93d572de..7fbe6512 100644
--- a/packages/metro-bundler/src/JSTransformer/worker/index.js
+++ b/packages/metro-bundler/src/JSTransformer/worker/index.js
@@ -19,6 +19,8 @@ const inline = require('./inline');
 const invariant = require('fbjs/lib/invariant');
 const minify = require('./minify');
 
+const {compactMapping} = require('../../Bundler/source-map');
+
 import type {LogEntry} from '../../Logger/Types';
 import type {MappingsMap} from '../../lib/SourceMap';
 import type {LocalPath} from '../../node-haste/lib/toLocalPath';
@@ -123,6 +125,11 @@ const transformCode: TransformCode = asyncify(
       src: sourceCode,
     });
 
+    // TODO: Add more robust check once the transformer only returns rawMappings
+    if (Array.isArray(transformed.map)) {
+      transformed.map = transformed.map.map(compactMapping);
+    }
+
     invariant(
       transformed != null,
       'Missing transform results despite having no error.',
diff --git a/packages/metro-bundler/src/transformer.js b/packages/metro-bundler/src/transformer.js
index a333c3a8..9fa1b589 100644
--- a/packages/metro-bundler/src/transformer.js
+++ b/packages/metro-bundler/src/transformer.js
@@ -24,8 +24,6 @@ const makeHMRConfig = require('babel-preset-react-native/configs/hmr');
 const path = require('path');
 const resolvePlugins = require('babel-preset-react-native/lib/resolvePlugins');
 
-const {compactMapping} = require('./Bundler/source-map');
-
 import type {Plugins as BabelPlugins} from 'babel-core';
 import type {Transformer, TransformOptions} from './JSTransformer/worker';
 
@@ -161,9 +159,7 @@ function transform({filename, options, src, plugins}: Params) {
         ast,
         code: result.code,
         filename,
-        map: options.generateSourceMaps
-          ? result.map
-          : result.rawMappings.map(compactMapping),
+        map: options.generateSourceMaps ? result.map : result.rawMappings,
       };
     }
   } finally {