diff --git a/src/su.c b/src/su.c
index d86aa86c..974048e9 100644
--- a/src/su.c
+++ b/src/su.c
@@ -379,7 +379,7 @@ static void prepare_pam_close_session (void)
 				/* wake child when resumed */
 				kill (pid, SIGCONT);
 				stop = false;
-			} else {
+			} else if (   (pid_t)-1 != pid) {
 				pid_child = 0;
 			}
 		} while (!stop);