diff --git a/trio/_core/_wakeup_socketpair.py b/trio/_core/_wakeup_socketpair.py
index 86eaeb6355..d78b1a506b 100644
--- a/trio/_core/_wakeup_socketpair.py
+++ b/trio/_core/_wakeup_socketpair.py
@@ -6,7 +6,7 @@
 from .. import _core
 from .._util import is_main_thread
 
-if sys.version_info >= (3, 7):
+if sys.version_info >= (3, 7) and '__pypy__' not in sys.builtin_module_names:
     HAVE_WARN_ON_FULL_BUFFER = True
 else:
     HAVE_WARN_ON_FULL_BUFFER = False