diff --git a/Modules/_posixsubprocess.c b/Modules/_posixsubprocess.c
--- a/Modules/_posixsubprocess.c
+++ b/Modules/_posixsubprocess.c
@@ -79,6 +79,11 @@
     } else if (p2cread != -1) {
         POSIX_CALL(dup2(p2cread, 0));  /* stdin */
     }
+    if (errwrite == 1) {
+        int olderrwrite = errwrite;
+        POSIX_CALL(errwrite = dup(errwrite));
+        close(olderrwrite);
+    }
     if (c2pwrite == 1) {
         int old = fcntl(c2pwrite, F_GETFD);
         if (old != -1)