diff --git a/js/xpconnect/loader/mozJSComponentLoader.cpp b/js/xpconnect/loader/mozJSComponentLoader.cpp
index 56d402f0e085..e5fcb38f1744 100644
--- a/js/xpconnect/loader/mozJSComponentLoader.cpp
+++ b/js/xpconnect/loader/mozJSComponentLoader.cpp
@@ -715,10 +715,16 @@ mozJSComponentLoader::ObjectForLocation(ComponentLoaderInfo& aInfo,
         // The script wasn't in the cache , so compile it now.
         LOG(("Slow loading %s\n", nativePath.get()));
 
+        // Note - if mReuseLoaderGlobal is true, then we can't do lazy source,
+        // because we compile things as functions (rather than script), and lazy
+        // source isn't supported in that configuration. That's ok though,
+        // because we only do mReuseLoaderGlobal on b2g, where we invoke
+        // setDiscardSource(true) on the entire global.
         CompileOptions options(cx);
         options.setNoScriptRval(mReuseLoaderGlobal ? false : true)
                .setVersion(JSVERSION_LATEST)
-               .setFileAndLine(nativePath.get(), 1);
+               .setFileAndLine(nativePath.get(), 1)
+               .setSourceIsLazy(!mReuseLoaderGlobal);
 
         if (realFile) {
 #ifdef HAVE_PR_MEMMAP