--- a/python/mozbuild/mozbuild/backend/recursivemake.py
+++ b/python/mozbuild/mozbuild/backend/recursivemake.py
@@ -1237,17 +1237,17 @@ INSTALL_TARGETS += %(prefix)s
 
         for lib in obj.linked_system_libs:
             if obj.KIND == 'target':
                 backend_file.write_once('OS_LIBS += %s\n' % lib)
             else:
                 backend_file.write_once('HOST_EXTRA_LIBS += %s\n' % lib)
 
         # Process library-based defines
-        self._process_defines(obj.defines, backend_file)
+        self._process_defines(obj.lib_defines, backend_file)
 
     def _process_final_target_files(self, obj, files, backend_file):
         target = obj.install_target
         path = mozpath.basedir(target, (
             'dist/bin',
             'dist/xpi-stage',
             '_tests',
             'dist/include',

--- a/python/mozbuild/mozbuild/frontend/data.py
+++ b/python/mozbuild/mozbuild/frontend/data.py
@@ -306,26 +306,26 @@ class ExampleWebIDLInterface(ContextDeri
 
 class LinkageWrongKindError(Exception):
     """Error thrown when trying to link objects of the wrong kind"""
 
 
 class Linkable(ContextDerived):
     """Generic context derived container object for programs and libraries"""
     __slots__ = (
-        'defines',
+        'lib_defines',
         'linked_libraries',
         'linked_system_libs',
     )
 
     def __init__(self, context):
         ContextDerived.__init__(self, context)
         self.linked_libraries = []
         self.linked_system_libs = []
-        self.defines = Defines(context, {})
+        self.lib_defines = Defines(context, {})
 
     def link_library(self, obj):
         assert isinstance(obj, BaseLibrary)
         if isinstance(obj, SharedLibrary) and obj.variant == obj.COMPONENT:
             raise LinkageWrongKindError(
                 'Linkable.link_library() does not take components.')
         if obj.KIND != self.KIND:
             raise LinkageWrongKindError('%s != %s' % (obj.KIND, self.KIND))

--- a/python/mozbuild/mozbuild/frontend/emitter.py
+++ b/python/mozbuild/mozbuild/frontend/emitter.py
@@ -239,27 +239,27 @@ class TreeMetadataEmitter(LoggingMixin):
                     'or a program, but USE_LIBS contains the following shared '
                     'library names:\n    %s\n\nMaybe you can remove the '
                     'static "%s" library?' % (lib.basename,
                     '\n    '.join(shared_libs), lib.basename),
                     contexts[lib.objdir])
 
         # Propagate LIBRARY_DEFINES to all child libraries recursively.
         def propagate_defines(outerlib, defines):
-            outerlib.defines.update(defines)
+            outerlib.lib_defines.update(defines)
             for lib in outerlib.linked_libraries:
                 # Propagate defines only along FINAL_LIBRARY paths, not USE_LIBS
                 # paths.
                 if (isinstance(lib, StaticLibrary) and
                         lib.link_into == outerlib.basename):
                     propagate_defines(lib, defines)
 
         for lib in (l for libs in self._libs.values() for l in libs):
             if isinstance(lib, Library):
-                propagate_defines(lib, lib.defines)
+                propagate_defines(lib, lib.lib_defines)
             yield lib
 
         for obj in self._binaries.values():
             yield obj
 
     LIBRARY_NAME_VAR = {
         'host': 'HOST_LIBRARY_NAME',
         'target': 'LIBRARY_NAME',
@@ -519,17 +519,17 @@ class TreeMetadataEmitter(LoggingMixin):
                 lib = StaticLibrary(context, libname, **static_args)
                 self._libs[libname].append(lib)
                 self._linkage.append((context, lib, 'USE_LIBS'))
 
             if lib_defines:
                 if not libname:
                     raise SandboxValidationError('LIBRARY_DEFINES needs a '
                         'LIBRARY_NAME to take effect', context)
-                lib.defines.update(lib_defines)
+                lib.lib_defines.update(lib_defines)
 
     def emit_from_context(self, context):
         """Convert a Context to tree metadata objects.
 
         This is a generator of mozbuild.frontend.data.ContextDerived instances.
         """
 
         # We only want to emit an InstallationTarget if one of the consulted

--- a/python/mozbuild/mozbuild/test/frontend/test_emitter.py
+++ b/python/mozbuild/mozbuild/test/frontend/test_emitter.py
@@ -729,17 +729,17 @@ class TestEmitterBasic(unittest.TestCase
         expected = {
             'liba': '-DIN_LIBA',
             'libb': '-DIN_LIBA -DIN_LIBB',
             'libc': '-DIN_LIBA -DIN_LIBB',
             'libd': ''
         }
         defines = {}
         for lib in libraries:
-            defines[lib.basename] = ' '.join(lib.defines.get_defines())
+            defines[lib.basename] = ' '.join(lib.lib_defines.get_defines())
         self.assertEqual(expected, defines)
 
     def test_sources(self):
         """Test that SOURCES works properly."""
         reader = self.reader('sources')
         objs = self.read_topsrcdir(reader)
 
         self.assertEqual(len(objs), 6)