diff --git a/telethon/full_sync.py b/telethon/full_sync.py
index 624e92f0..5f72d1df 100644
--- a/telethon/full_sync.py
+++ b/telethon/full_sync.py
@@ -51,7 +51,8 @@ class _SyncGen:
             raise StopIteration from None
 
 
-def _syncify_wrap(t, method_name, loop, thread_ident, syncifier=_sync_result):
+def _syncify_wrap(t, method_name, loop, thread_ident,
+                  syncifier=_sync_result, rename=None):
     method = getattr(t, method_name)
 
     @functools.wraps(method)
@@ -62,11 +63,25 @@ def _syncify_wrap(t, method_name, loop, thread_ident, syncifier=_sync_result):
             else syncifier(loop, coro)
         )
 
-    setattr(t, method_name, syncified)
+    setattr(t, rename or method_name, syncified)
 
 
 def _syncify(*types, loop, thread_ident):
     for t in types:
+        # __enter__ and __exit__ need special care (VERY dirty hack).
+        #
+        # Normally we want them to raise if the loop is running because
+        # the user can't await there, and they need the async with variant.
+        #
+        # However they check if the loop is running to raise, which it is
+        # with full_sync enabled, so we patch them with the async variant.
+        if hasattr(t, '__aenter__'):
+            _syncify_wrap(
+                t, '__aenter__', loop, thread_ident, rename='__enter__')
+
+            _syncify_wrap(
+                t, '__aexit__', loop, thread_ident, rename='__exit__')
+
         for name in dir(t):
             if not name.startswith('_') or name == '__call__':
                 meth = getattr(t, name)