diff --git a/python/mozbuild/mozbuild/frontend/data.py b/python/mozbuild/mozbuild/frontend/data.py
index 959f6a42301e2a..6e44938f333aad 100644
--- a/python/mozbuild/mozbuild/frontend/data.py
+++ b/python/mozbuild/mozbuild/frontend/data.py
@@ -185,10 +185,11 @@ def __init__(self, sandbox, defines):
     def get_defines(self):
         for define, value in self.defines.iteritems():
             if value is True:
-                defstr = define
+                yield('-D%s' % define)
+            elif value is False:
+                yield('-U%s' % define)
             else:
-                defstr = '%s=%s' % (define, shell_quote(value))
-            yield('-D%s' % defstr)
+                yield('-D%s=%s' % (define, shell_quote(value)))
 
 class Exports(SandboxDerived):
     """Sandbox container object for EXPORTS, which is a HierarchicalStringList.
diff --git a/python/mozbuild/mozbuild/test/backend/data/defines/moz.build b/python/mozbuild/mozbuild/test/backend/data/defines/moz.build
index 29cc9735cec5b8..be4b3114348226 100644
--- a/python/mozbuild/mozbuild/test/backend/data/defines/moz.build
+++ b/python/mozbuild/mozbuild/test/backend/data/defines/moz.build
@@ -9,5 +9,6 @@ DEFINES = {
 DEFINES['BAZ'] = '"ab\'cd"'
 DEFINES.update({
     'BAR': 7,
-    'VALUE': value
+    'VALUE': value,
+    'QUX': False,
 })
diff --git a/python/mozbuild/mozbuild/test/backend/test_recursivemake.py b/python/mozbuild/mozbuild/test/backend/test_recursivemake.py
index 86519dbd7938c7..191a744af7f73e 100644
--- a/python/mozbuild/mozbuild/test/backend/test_recursivemake.py
+++ b/python/mozbuild/mozbuild/test/backend/test_recursivemake.py
@@ -524,7 +524,7 @@ def test_defines(self):
         var = 'DEFINES'
         defines = [val for val in lines if val.startswith(var)]
 
-        expected = ['DEFINES += -DFOO -DBAZ=\'"ab\'\\\'\'cd"\' -DBAR=7 -DVALUE=\'xyz\'']
+        expected = ['DEFINES += -DFOO -DBAZ=\'"ab\'\\\'\'cd"\' -UQUX -DBAR=7 -DVALUE=\'xyz\'']
         self.assertEqual(defines, expected)
 
     def test_local_includes(self):
diff --git a/python/mozbuild/mozbuild/test/frontend/data/defines/moz.build b/python/mozbuild/mozbuild/test/frontend/data/defines/moz.build
index 240eb70315b564..ccb0d5e3606cfe 100644
--- a/python/mozbuild/mozbuild/test/frontend/data/defines/moz.build
+++ b/python/mozbuild/mozbuild/test/frontend/data/defines/moz.build
@@ -9,5 +9,6 @@ DEFINES = {
 DEFINES['BAZ'] = '"abcd"'
 DEFINES.update({
     'BAR': 7,
-    'VALUE': value
+    'VALUE': value,
+    'QUX': False,
 })
diff --git a/python/mozbuild/mozbuild/test/frontend/test_emitter.py b/python/mozbuild/mozbuild/test/frontend/test_emitter.py
index 730dea7a31a476..18b5d11fbcb63b 100644
--- a/python/mozbuild/mozbuild/test/frontend/test_emitter.py
+++ b/python/mozbuild/mozbuild/test/frontend/test_emitter.py
@@ -532,6 +532,7 @@ def test_defines(self):
             'BAZ': '"abcd"',
             'FOO': True,
             'VALUE': 'xyz',
+            'QUX': False,
         }
 
         self.assertEqual(defines, expected)