--- a/dom/canvas/moz.build
+++ b/dom/canvas/moz.build
@@ -196,17 +196,16 @@ LOCAL_INCLUDES += [
     '/js/xpconnect/wrappers',
 ]
 
 include('/ipc/chromium/chromium-config.mozbuild')
 
 FINAL_LIBRARY = 'xul'
 LOCAL_INCLUDES += [
     '../workers',
-    '/', # Allow including relpaths from root.
     '/dom/base',
     '/dom/html',
     '/dom/svg',
     '/dom/workers',
     '/dom/xul',
     '/gfx/gl',
     '/image',
     '/js/xpconnect/src',

--- a/media/webrtc/trunk/gtest/moz.build
+++ b/media/webrtc/trunk/gtest/moz.build
@@ -16,17 +16,16 @@ DEFINES['WEBRTC_APM_DEBUG_DUMP'] = True
 DEFINES['WEBRTC_INTELLIGIBILITY_ENHANCER'] = 0
 DEFINES['WEBRTC_MOZILLA_BUILD'] = 1
 
 # Hit build errors on windows with xutility otherwise
 DisableStlWrapping()
 
 LOCAL_INCLUDES += [
     '../',
-    '/',
     '/ipc/chromium/src/',
     '/media/libopus/celt/',
     '/media/libopus/include',
     '/media/libopus/src',
     '/media/libyuv/libyuv/include',
 ]
 
 USE_LIBS += [

--- a/python/mozbuild/mozbuild/frontend/emitter.py
+++ b/python/mozbuild/mozbuild/frontend/emitter.py
@@ -1116,21 +1116,27 @@ class TreeMetadataEmitter(LoggingMixin):
             ('WEBIDL_EXAMPLE_INTERFACES', ExampleWebIDLInterface),
         ]
         for context_var, klass in simple_lists:
             for name in context.get(context_var, []):
                 yield klass(context, name)
 
         local_includes = []
         for local_include in context.get('LOCAL_INCLUDES', []):
+            full_path = local_include.full_path
             if (not isinstance(local_include, ObjDirPath) and
-                    not os.path.exists(local_include.full_path)):
+                    not os.path.exists(full_path)):
                 raise SandboxValidationError('Path specified in LOCAL_INCLUDES '
                     'does not exist: %s (resolved to %s)' % (local_include,
-                    local_include.full_path), context)
+                    full_path), context)
+            if (full_path == context.config.topsrcdir or
+                    full_path == context.config.topobjdir):
+                raise SandboxValidationError('Path specified in LOCAL_INCLUDES '
+                    'is not allowed: %s (resolved to %s)' % (local_include,
+                    full_path), context)
             include_obj = LocalInclude(context, local_include)
             local_includes.append(include_obj.path.full_path)
             yield include_obj
 
         computed_flags.resolve_flags('LOCAL_INCLUDES', ['-I%s' % p for p in local_includes])
         computed_as_flags.resolve_flags('LOCAL_INCLUDES', ['-I%s' % p for p in local_includes])
         computed_host_flags.resolve_flags('LOCAL_INCLUDES', ['-I%s' % p for p in local_includes])
 

new file mode 100644
--- /dev/null
+++ b/python/mozbuild/mozbuild/test/frontend/data/local_includes-invalid/objdir/moz.build
@@ -0,0 +1,5 @@
+# -*- Mode: python; indent-tabs-mode: nil; tab-width: 40 -*-
+# Any copyright is dedicated to the Public Domain.
+# http://creativecommons.org/publicdomain/zero/1.0/
+
+LOCAL_INCLUDES += ['!/']

new file mode 100644
--- /dev/null
+++ b/python/mozbuild/mozbuild/test/frontend/data/local_includes-invalid/srcdir/moz.build
@@ -0,0 +1,5 @@
+# -*- Mode: python; indent-tabs-mode: nil; tab-width: 40 -*-
+# Any copyright is dedicated to the Public Domain.
+# http://creativecommons.org/publicdomain/zero/1.0/
+
+LOCAL_INCLUDES += ['/']

--- a/python/mozbuild/mozbuild/test/frontend/test_emitter.py
+++ b/python/mozbuild/mozbuild/test/frontend/test_emitter.py
@@ -967,16 +967,32 @@ class TestEmitterBasic(unittest.TestCase
                           for o in objs if isinstance(o, LocalInclude)]
         expected = [
             mozpath.join(reader.config.topsrcdir, 'bar/baz'),
             mozpath.join(reader.config.topsrcdir, 'foo'),
         ]
 
         self.assertEqual(local_includes, expected)
 
+    def test_local_includes_invalid(self):
+        """Test that invalid LOCAL_INCLUDES are properly detected."""
+        reader = self.reader('local_includes-invalid/srcdir')
+
+        with self.assertRaisesRegexp(
+                SandboxValidationError,
+                'Path specified in LOCAL_INCLUDES is not allowed:'):
+            objs = self.read_topsrcdir(reader)
+
+        reader = self.reader('local_includes-invalid/objdir')
+
+        with self.assertRaisesRegexp(
+                SandboxValidationError,
+                'Path specified in LOCAL_INCLUDES is not allowed:'):
+            objs = self.read_topsrcdir(reader)
+
     def test_generated_includes(self):
         """Test that GENERATED_INCLUDES is emitted correctly."""
         reader = self.reader('generated_includes')
         objs = self.read_topsrcdir(reader)
 
         generated_includes = [o.path for o in objs if isinstance(o, LocalInclude)]
         expected = [
             '!/bar/baz',