Index: lib/libc/gen/posix_spawn.c
===================================================================
--- lib/libc/gen/posix_spawn.c
+++ lib/libc/gen/posix_spawn.c
@@ -161,15 +161,21 @@
 					return (EBADF);
 			}
 		}
-		if (_fcntl(fae->fae_fildes, F_SETFD, 0) == -1)
-			return (errno);
 		break;
 	case FAE_DUP2:
-		/* Perform a dup2() */
-		if (_dup2(fae->fae_fildes, fae->fae_newfildes) == -1)
-			return (errno);
-		if (_fcntl(fae->fae_newfildes, F_SETFD, 0) == -1)
+		/*
+		 * Perform a dup2(), except when we don't really need to.  If
+		 * old == new, dup2() will return successfully and leave the
+		 * CLOEXEC flag untouched.  Avoid it and just unconditionally
+		 * clear the CLOEXEC flag.  If we really do dup2(), the CLOEXEC
+		 * flag is cleared already.
+		 */
+		if (fae->fae_fildes == fae->fae_newfildes) {
+			if (_fcntl(fae->fae_newfildes, F_SETFD, 0) == -1)
+				return (errno);
+		} else if (_dup2(fae->fae_fildes, fae->fae_newfildes) == -1) {
 			return (errno);
+		}
 		break;
 	case FAE_CLOSE:
 		/* Perform a close(), do not fail if already closed */
@@ -384,7 +390,7 @@
 		return (error);
 	}
 	fae->fae_fildes = fildes;
-	fae->fae_oflag = oflag;
+	fae->fae_oflag = oflag & ~O_CLOEXEC;
 	fae->fae_mode = mode;
 
 	STAILQ_INSERT_TAIL(&(*fa)->fa_list, fae, fae_list);