diff --git a/build/ppCheck.py b/build/ppCheck.py
new file mode 100644
index 000000000..1e27ca171
--- /dev/null
+++ b/build/ppCheck.py
@@ -0,0 +1,72 @@
+#!/usr/bin/env python
+
+from __future__ import print_function
+import os, sys
+
+if not len(sys.argv) is 2 or not os.path.exists(sys.argv[1]):
+  print("\nYou did not supply a valid path to check.")
+  exit(1)
+else:
+  print("\nChecking for un-preprocessed files...", end = ' ')
+  DIST_PATH = sys.argv[1]
+
+PP_FILE_TYPES = (
+  '.css',
+  '.dtd',
+  '.html',
+  '.js',
+  '.jsm',
+  '.xhtml',
+  '.xml',
+  '.xul',
+  '.manifest',
+  '.properties',
+  '.rdf'
+)
+
+PP_SPECIAL_TYPES = ('.css')
+
+PP_DIRECTIVES = [
+  'define',
+  'if',
+  'ifdef',
+  'ifndef',
+  'elif',
+  'elifdef',
+  'endif',
+  'error',
+  'expand',
+  'filter',
+  'include',
+  'literal',
+  'undef',
+  'unfilter'
+]
+
+PP_FILES = []
+PP_BAD_FILES = []
+
+for root, directories, filenames in os.walk(DIST_PATH):
+  for filename in filenames: 
+    if filename.endswith(PP_FILE_TYPES):
+      PP_FILES += [ os.path.join(root, filename).replace(os.sep, '/') ]
+
+for file in PP_FILES:
+  with open(file) as fp:
+    marker = '%' if file.endswith(PP_SPECIAL_TYPES) else '#'
+    directives = tuple(marker + directive for directive in PP_DIRECTIVES)
+    for line in fp:
+      if line.startswith(directives):
+        PP_BAD_FILES += [ file.replace(DIST_PATH + '/', '') ]
+  fp.close()
+
+PP_BAD_FILES = list(dict.fromkeys(PP_BAD_FILES))
+
+print('Done!')
+
+if len(PP_BAD_FILES) > 0:
+  print("\nWARNING: The following {0} file(s) in {1} may require preprocessing:\n".format(len(PP_BAD_FILES), DIST_PATH))
+  for file in PP_BAD_FILES:
+    print(file)
+
+exit(0)
\ No newline at end of file
diff --git a/python/mozbuild/mozbuild/mach_commands.py b/python/mozbuild/mozbuild/mach_commands.py
index 5933a5aa9..bd3fbe921 100644
--- a/python/mozbuild/mozbuild/mach_commands.py
+++ b/python/mozbuild/mozbuild/mach_commands.py
@@ -541,20 +541,24 @@ class Build(MachCommandBase):
                 # as when doing OSX Universal builds)
                 pass
 
-        # Check if there are any unpreprocessed files in '@MOZ_OBJDIR@/dist/bin'
-        # See python/mozbuild/mozbuild/preprocessor.py#L293-L309 for the list of directives
-        # We skip if, ifdef, ifndef, else, elif, elifdef and elifndef, because they are never used alone
-        #
-        # The original version of this script only worked with GNU grep because of the --include flag. 
-        # Not a problem in and of itself, except that it didn't take TOOLCHAIN_PREFIX and simply assumed 
-        # all operating systems use GNU grep as the system grep (often it's called ggrep or something). 
-        # This script is a bit slower, but should do the same thing on all Unix platforms. 
+        # Check for un-preprocessed files.. In case something goes wrong it will be noted
+        ppcheck_script = mozpath.join(self.topsrcdir, "build", "ppCheck.py")
+        ppcheck_path = mozpath.join(self.topobjdir, "dist", "bin")
+        if not os.path.exists(ppcheck_script):
+            ppcheck_script = mozpath.join(self.topsrcdir, "mozilla", "build", "ppCheck.py")
 
-        grepcmd = 'find ' + self.topobjdir + '/dist/bin' + ' -name \'\*.{css,dtd,html,js,jsm,xhtml,xml,xul,manifest,properties,rdf}\' ' + '| xargs grep -E "^(#|%)(define|endif|error|expand|filter|include|literal|undef|unfilter)" '\
-                  + '| awk "/\.css:%/ || (!/\.css/ && /:#/)"'
-        grepresult = subprocess.Popen(grepcmd, stdout=subprocess.PIPE, shell=True).communicate()[0]
-        if grepresult:
-            print('\nERROR: preprocessor was not applied to the following files:\n\n' + grepresult)
+        if not os.path.exists(ppcheck_script):
+            ppcheck_script = mozpath.join(self.topsrcdir, "platform", "build", "ppCheck.py")
+        else:
+            ppcheck_script = None
+        
+        if ppcheck_script:
+            ppcheck_cmd = [which.which("python2.7"), ppcheck_script, ppcheck_path]
+            ppcheck_result = subprocess.call(ppcheck_cmd, cwd=self.topsrcdir)
+        
+        if not ppcheck_script or ppcheck_result: 
+            print("\nWARNING: Something has gone wrong with the check for un-preprocessed files. " +
+                  "Please manually verify that files are properly preprocessed.")
 
         return status