diff --git a/python/mozbuild/mozbuild/jar.py b/python/mozbuild/mozbuild/jar.py
index 97d366057a8..a53daf0f5f3 100644
--- a/python/mozbuild/mozbuild/jar.py
+++ b/python/mozbuild/mozbuild/jar.py
@@ -253,21 +253,6 @@ class JarMaker(object):
                      )
         return p
 
-    def processIncludes(self, includes):
-        '''Process given includes with the inner PreProcessor.
-
-        Only use this for #defines, the includes shouldn't generate
-        content.
-        '''
-
-        self.pp.out = StringIO()
-        for inc in includes:
-            self.pp.do_include(inc)
-        includesvalue = self.pp.out.getvalue()
-        if includesvalue:
-            logging.info('WARNING: Includes produce non-empty output')
-        self.pp.out = None
-
     def finalizeJar(self, jardir, jarbase, jarname, chromebasepath, register, doZip=True):
         '''Helper method to write out the chrome registration entries to
          jarfile.manifest or chrome.manifest, or both.
@@ -560,7 +545,6 @@ def main(args=None):
     jm = JarMaker()
     p = jm.getCommandLineParser()
     (options, args) = p.parse_args(args)
-    jm.processIncludes(options.I)
     jm.outputFormat = options.f
     jm.sourcedirs = options.s
     jm.topsourcedir = options.t
diff --git a/python/mozbuild/mozbuild/preprocessor.py b/python/mozbuild/mozbuild/preprocessor.py
index 6a49ee87011..8cc35cda711 100644
--- a/python/mozbuild/mozbuild/preprocessor.py
+++ b/python/mozbuild/mozbuild/preprocessor.py
@@ -456,7 +456,6 @@ class Preprocessor:
         options, args = p.parse_args(args=args)
         out = self.out
         depfile = None
-        includes = options.I
 
         if options.output:
             out = get_output_file(options.output)
@@ -475,10 +474,9 @@ class Preprocessor:
                 raise Preprocessor.Error(self, "--depend requires the "
                                                "mozbuild.makeutil module", None)
             depfile = get_output_file(options.depend)
-        includes.extend(args)
 
-        if includes:
-            for f in includes:
+        if args:
+            for f in args:
                 with open(f, 'rU') as input:
                     self.processFile(input=input, output=out)
             if depfile:
@@ -512,8 +510,6 @@ class Preprocessor:
         def handleSilenceDirectiveWarnings(option, opt, value, parse):
             self.setSilenceDirectiveWarnings(True)
         p = OptionParser()
-        p.add_option('-I', action='append', type="string", default = [],
-                     metavar="FILENAME", help='Include file')
         p.add_option('-D', action='callback', callback=handleD, type="string",
                      metavar="VAR[=VAL]", help='Define a variable')
         p.add_option('-U', action='callback', callback=handleU, type="string",