diff --git a/python/mozbuild/mozbuild/base.py b/python/mozbuild/mozbuild/base.py
index 66edad6563c..1db94c75eb7 100644
--- a/python/mozbuild/mozbuild/base.py
+++ b/python/mozbuild/mozbuild/base.py
@@ -421,6 +421,26 @@ class MozbuildObject(ProcessExecutionMixin):
         if filename:
             args.extend(['-f', filename])
 
+        if num_jobs == 0 and self.mozconfig['make_flags']:
+            flags = iter(self.mozconfig['make_flags'])
+            for flag in flags:
+                if flag == '-j':
+                    try:
+                        flag = flags.next()
+                    except StopIteration:
+                        break
+                    try:
+                        num_jobs = int(flag)
+                    except ValueError:
+                        args.append(flag)
+                elif flag.startswith('-j'):
+                    try:
+                        num_jobs = int(flag[2:])
+                    except (ValueError, IndexError):
+                        break
+                else:
+                    args.append(flag)
+
         if allow_parallel:
             if num_jobs > 0:
                 args.append('-j%d' % num_jobs)