diff --git a/Lib/asyncio/unix_events.py b/Lib/asyncio/unix_events.py
index e4f445e95026b5..a55b3a375fa22d 100644
--- a/Lib/asyncio/unix_events.py
+++ b/Lib/asyncio/unix_events.py
@@ -126,7 +126,7 @@ def add_signal_handler(self, sig, callback, *args):
                     logger.info('set_wakeup_fd(-1) failed: %s', nexc)
 
             if exc.errno == errno.EINVAL:
-                raise RuntimeError(f'sig {sig} cannot be caught')
+                raise RuntimeError(f'sig {sig:d} cannot be caught')
             else:
                 raise
 
@@ -160,7 +160,7 @@ def remove_signal_handler(self, sig):
             signal.signal(sig, handler)
         except OSError as exc:
             if exc.errno == errno.EINVAL:
-                raise RuntimeError(f'sig {sig} cannot be caught')
+                raise RuntimeError(f'sig {sig:d} cannot be caught')
             else:
                 raise