diff --git a/docs/internals.rst b/docs/internals.rst
index e2281a47..5dbf431f 100644
--- a/docs/internals.rst
+++ b/docs/internals.rst
@@ -352,21 +352,18 @@ Helper Functions
 
 .. currentmodule:: mitogen.master
 
-.. function:: get_child_modules (path, fullname)
+.. function:: get_child_modules (path)
 
-    Return the canonical names of all submodules of a package `module`.
+    Return the suffixes of submodules directly neated beneath of the package
+    directory at `path`.
 
     :param str path:
         Path to the module's source code on disk, or some PEP-302-recognized
         equivalent. Usually this is the module's ``__file__`` attribute, but
         is specified explicitly to avoid loading the module.
 
-    :param str fullname:
-        The module's canonical name. This is the module's ``__name__``
-        attribute, but is specified explicitly to avoid loading the module.
-
     :return:
-        List of canonical submodule names.
+        List of submodule name suffixes.
 
 
 .. currentmodule:: mitogen.parent
diff --git a/mitogen/core.py b/mitogen/core.py
index 36661b96..2e1ad8aa 100644
--- a/mitogen/core.py
+++ b/mitogen/core.py
@@ -402,14 +402,14 @@ class Importer(object):
     def __init__(self, router, context, core_src, whitelist=(), blacklist=()):
         self._context = context
         self._present = {'mitogen': [
-            'mitogen.compat',
-            'mitogen.compat.pkgutil',
-            'mitogen.fakessh',
-            'mitogen.master',
-            'mitogen.parent',
-            'mitogen.ssh',
-            'mitogen.sudo',
-            'mitogen.utils',
+            'compat',
+            'compat.pkgutil',
+            'fakessh',
+            'master',
+            'parent',
+            'ssh',
+            'sudo',
+            'utils',
         ]}
         self._lock = threading.Lock()
         self.whitelist = whitelist or ['']
@@ -444,9 +444,10 @@ class Importer(object):
         _tls.running = True
         fullname = fullname.rstrip('.')
         try:
-            pkgname, _, _ = fullname.rpartition('.')
+            pkgname, dot, _ = fullname.rpartition('.')
             _v and LOG.debug('%r.find_module(%r)', self, fullname)
-            if fullname not in self._present.get(pkgname, (fullname,)):
+            suffix = fullname[len(pkgname+dot):]
+            if suffix not in self._present.get(pkgname, (suffix,)):
                 _v and LOG.debug('%r: master doesn\'t know %r', self, fullname)
                 return None
 
diff --git a/mitogen/master.py b/mitogen/master.py
index 6fbfaf8a..a0a85a8e 100644
--- a/mitogen/master.py
+++ b/mitogen/master.py
@@ -56,9 +56,9 @@ from mitogen.core import LOG
 RLOG = logging.getLogger('mitogen.ctx')
 
 
-def get_child_modules(path, fullname):
+def get_child_modules(path):
     it = pkgutil.iter_modules([os.path.dirname(path)])
-    return ['%s.%s' % (fullname, name) for _, name, _ in it]
+    return [name for _, name, _ in it]
 
 
 def scan_code_imports(co, LOAD_CONST=dis.opname.index('LOAD_CONST'),
@@ -489,7 +489,7 @@ class ModuleResponder(object):
             raise ImportError('could not find %r' % (fullname,))
 
         if is_pkg:
-            pkg_present = get_child_modules(path, fullname)
+            pkg_present = get_child_modules(path)
             LOG.debug('_build_tuple(%r, %r) -> %r',
                       path, fullname, pkg_present)
         else: