diff --git a/app/src/main/cpp/fakeinput_steam.cpp b/app/src/main/cpp/fakeinput_steam.cpp
index c446170fe..a1bc4ab17 100644
--- a/app/src/main/cpp/fakeinput_steam.cpp
+++ b/app/src/main/cpp/fakeinput_steam.cpp
@@ -2936,15 +2936,19 @@ EXPORT DIR *opendir(const char *name) {
   return dir;
 }
 
+static bool open_has_mode(int flags) {
+  return (flags & O_CREAT) != 0 || (flags & O_TMPFILE) == O_TMPFILE;
+}
+
 EXPORT int open(const char *pathname, int flags, ...) {
   va_list va;
-  mode_t mode;
+  mode_t mode = 0;
   int fd;
   bool hasMode;
 
   va_start(va, flags);
 
-  hasMode = flags & O_CREAT;
+  hasMode = open_has_mode(flags);
 
   if (hasMode) {
     mode = va_arg(va, mode_t);
@@ -3016,13 +3020,13 @@ EXPORT int open(const char *pathname, int flags, ...) {
 
 EXPORT int openat(int dirfd, const char *pathname, int flags, ...) {
   va_list va;
-  mode_t mode;
+  mode_t mode = 0;
   int fd;
   bool hasMode;
 
   va_start(va, flags);
 
-  hasMode = flags & O_CREAT;
+  hasMode = open_has_mode(flags);
 
   if (hasMode) {
     mode = va_arg(va, mode_t);
@@ -4143,7 +4147,7 @@ EXPORT int select(int nfds, fd_set *readfds, fd_set *writefds,
 
 #ifdef __GLIBC__
 static mode_t open_mode(int flags, va_list va) {
-  return (flags & (O_CREAT | O_TMPFILE)) ? va_arg(va, mode_t) : 0;
+  return open_has_mode(flags) ? va_arg(va, mode_t) : 0;
 }
 
 EXPORT int open64(const char *pathname, int flags, ...) {
diff --git a/tools/tests/test_fakeinput_open.py b/tools/tests/test_fakeinput_open.py
new file mode 100644
index 000000000..f4853e30e
--- /dev/null
+++ b/tools/tests/test_fakeinput_open.py
@@ -0,0 +1,103 @@
+import os
+from pathlib import Path
+import shutil
+import subprocess
+import sys
+import tempfile
+import unittest
+
+SOURCE = Path(__file__).resolve().parents[2] / "app/src/main/cpp/fakeinput_steam.cpp"
+
+PROGRAM = r"""
+#define _GNU_SOURCE
+#include <assert.h>
+#include <dlfcn.h>
+#include <errno.h>
+#include <fcntl.h>
+#include <stdio.h>
+#include <string.h>
+#include <sys/stat.h>
+#include <unistd.h>
+
+int main(int argc, char **argv) {
+    assert(argc == 4);
+    void *symbol = dlsym(RTLD_DEFAULT, argv[1]);
+    assert(symbol);
+    int (*plain)(const char *, int, ...) = symbol;
+    int (*at)(int, const char *, int, ...) = symbol;
+    int relative = strstr(argv[1], "at") != NULL;
+    int temporary = !strcmp(argv[2], "temporary");
+    int directory = !strcmp(argv[2], "directory");
+    int dirfd = open(argv[3], O_RDONLY | O_DIRECTORY);
+    assert(dirfd >= 0);
+    assert(fchdir(dirfd) == 0);
+    umask(0);
+    const char *path = temporary || directory ? "." : "created";
+    int flags = directory ? O_RDONLY | O_DIRECTORY : O_RDWR | (temporary ? O_TMPFILE : O_CREAT | O_EXCL);
+    int fd;
+    if (directory) fd = relative ? at(dirfd, path, flags) : plain(path, flags);
+    else fd = relative ? at(dirfd, path, flags, 0640) : plain(path, flags, 0640);
+    if (temporary && fd < 0 && (errno == EOPNOTSUPP || errno == EINVAL)) return 77;
+    assert(fd >= 0);
+    struct stat st;
+    assert(fstat(fd, &st) == 0);
+    if (directory) assert(S_ISDIR(st.st_mode));
+    else {
+        if ((st.st_mode & 0777) != 0640) {
+            fprintf(stderr, "%s %s: expected mode 640, got %o\n", argv[1], argv[2], st.st_mode & 0777);
+            return 1;
+        }
+        assert(write(fd, "ok", 2) == 2);
+        assert(lseek(fd, 0, SEEK_SET) == 0);
+        char bytes[2];
+        assert(read(fd, bytes, 2) == 2 && !memcmp(bytes, "ok", 2));
+    }
+    close(fd);
+    close(dirfd);
+    return 0;
+}
+"""
+
+
+@unittest.skipUnless(sys.platform == "linux" and shutil.which("gcc") and shutil.which("g++"),
+                     "needs Linux, gcc and g++")
+class FakeinputOpenTest(unittest.TestCase):
+    @classmethod
+    def setUpClass(cls):
+        cls.tmp = tempfile.TemporaryDirectory()
+        cls.addClassCleanup(cls.tmp.cleanup)
+        cls.path = Path(cls.tmp.name)
+        source = cls.path / "program.c"
+        source.write_text(PROGRAM)
+        subprocess.run(["gcc", "-o", str(cls.path / "program"), str(source), "-ldl"], check=True)
+        subprocess.run(["g++", "-shared", "-fPIC", "-O2", "-Wno-attributes", "-pthread",
+                        "-std=c++17", "-static-libstdc++", "-static-libgcc",
+                        "-Wl,--exclude-libs,ALL", "-o", str(cls.path / "libfakeinput.so"),
+                        str(SOURCE), "-ldl"], check=True)
+
+    def check_open(self, kind):
+        for function in ("open", "openat", "open64", "openat64"):
+            with self.subTest(function=function), tempfile.TemporaryDirectory() as directory:
+                args = [str(self.path / "program"), function, kind, directory]
+                baseline = subprocess.run(args, capture_output=True, text=True)
+                if baseline.returncode == 77:
+                    self.skipTest("filesystem does not support O_TMPFILE")
+                self.assertEqual(baseline.returncode, 0, baseline.stderr)
+                if kind == "named":
+                    (Path(directory) / "created").unlink()
+                result = subprocess.run(args, env=dict(os.environ, LD_PRELOAD=str(self.path / "libfakeinput.so")),
+                                        capture_output=True, text=True, timeout=10)
+                self.assertEqual(result.returncode, 0, result.stderr)
+
+    def test_unnamed_temporary_files_keep_requested_permissions(self):
+        self.check_open("temporary")
+
+    def test_named_files_keep_requested_permissions(self):
+        self.check_open("named")
+
+    def test_directory_opens_do_not_need_a_mode_argument(self):
+        self.check_open("directory")
+
+
+if __name__ == "__main__":
+    unittest.main()