diff --git a/local-cli/bundle/buildBundle.js b/local-cli/bundle/buildBundle.js
index 66fad891a..36081a605 100644
--- a/local-cli/bundle/buildBundle.js
+++ b/local-cli/bundle/buildBundle.js
@@ -100,7 +100,7 @@ async function buildBundle(
     providesModuleNodeModules: providesModuleNodeModules,
     resetCache: args.resetCache,
     reporter: new TerminalReporter(terminal),
-    sourceExts: defaultSourceExts.concat(sourceExts),
+    sourceExts: sourceExts.concat(defaultSourceExts),
     transformCache: TransformCaching.useTempDir(),
     transformModulePath: transformModulePath,
     watch: false,
diff --git a/local-cli/server/runServer.js b/local-cli/server/runServer.js
index 396c57ce6..8054190e1 100644
--- a/local-cli/server/runServer.js
+++ b/local-cli/server/runServer.js
@@ -187,7 +187,7 @@ function getPackagerServer(args, config, reporter) {
     providesModuleNodeModules: providesModuleNodeModules,
     reporter,
     resetCache: args.resetCache,
-    sourceExts: defaultSourceExts.concat(args.sourceExts),
+    sourceExts: args.sourceExts.concat(defaultSourceExts),
     transformModulePath: transformModulePath,
     transformCache: TransformCaching.useTempDir(),
     verbose: args.verbose,