--- a/python/mozbuild/mozbuild/configure/__init__.py
+++ b/python/mozbuild/mozbuild/configure/__init__.py
@@ -286,21 +286,19 @@ class ConfigureSandbox(dict):
         references. The decorated function is called as soon as the decorator
         is called, and the arguments it receives are the OptionValue or
         function results corresponding to each of the arguments to @depends.
         As an exception, when a HelpFormatter is attached, only functions that
         have '--help' in their @depends argument list are called.
 
         The decorated function is altered to use a different global namespace
         for its execution. This different global namespace exposes a limited
-        set of functions from os.path, and two additional functions:
-        `imply_option` and `set_define`. The former allows to inject
-        additional options as if they had been passed on the command line.
-        The latter declares new defines, stored in a DEFINES configuration
-        item.
+        set of functions from os.path, and one additional functions:
+        `imply_option`. It allows to inject additional options as if they had
+        been passed on the command line.
         '''
         if not args:
             raise ConfigureError('@depends needs at least one argument')
 
         with_help = False
         resolved_args = []
         for arg in args:
             if isinstance(arg, types.StringTypes):
@@ -330,17 +328,16 @@ class ConfigureSandbox(dict):
         def decorator(func):
             if inspect.isgeneratorfunction(func):
                 raise ConfigureError(
                     'Cannot decorate generator functions with @depends')
             func, glob = self._prepare_function(func)
             result = DependsOutput()
             glob.update(
                 imply_option=result.imply_option,
-                set_define=self._set_define,
             )
             dummy = wraps(func)(DummyFunction())
             self._depends[dummy] = func
             func.with_help = with_help
             if with_help:
                 for arg in args:
                     if (isinstance(arg, DummyFunction) and
                             not self._depends[arg].with_help):
@@ -453,22 +450,16 @@ class ConfigureSandbox(dict):
         `value` can be references to @depends functions, in which case the
         result from these functions is used. If the result of such functions
         is None, the define is not set. If the result is False, the define is
         explicitly undefined (-U).
         '''
         defines = self._config.setdefault('DEFINES', {})
         self._resolve_and_set(defines, name, value)
 
-    def _set_define(self, name, value):
-        defines = self._config.setdefault('DEFINES', {})
-        if name in defines:
-            raise ConfigureError("'%s' is already defined" % name)
-        defines[name] = value
-
     def _prepare_function(self, func):
         '''Alter the given function global namespace with the common ground
         for @depends, @template and @advanced.
         '''
         if not inspect.isfunction(func):
             raise TypeError("Unexpected type: '%s'" % type(func))
         if func in self._prepared_functions:
             return func, func.func_globals