diff --git a/process.c b/process.c
index 4388a6ba0f..08986f9ede 100644
--- a/process.c
+++ b/process.c
@@ -1114,6 +1114,8 @@ waitpid_no_SIGCHLD(struct waitpid_state *w)
                                        RUBY_UBF_PROCESS, 0);
         } while (w->ret < 0 && errno == EINTR && (RUBY_VM_CHECK_INTS(w->ec),1));
     }
+    if (w->ret == -1)
+        w->errnum = errno;
 }
 
 rb_pid_t