--- a/python/mozbuild/mozpack/files.py
+++ b/python/mozbuild/mozpack/files.py
@@ -486,16 +486,19 @@ class GeneratedFile(BaseFile):
     File class for content with no previous existence on the filesystem.
     '''
     def __init__(self, content):
         self.content = content
 
     def open(self):
         return BytesIO(self.content)
 
+    def read(self):
+        return self.content
+
 
 class DeflatedFile(BaseFile):
     '''
     File class for members of a jar archive. DeflatedFile.copy() effectively
     extracts the file from the jar archive.
     '''
     def __init__(self, file):
         from mozpack.mozjar import JarFileReader