diff --git a/core/libs/prx/libkernel/File/src/Open.cpp b/core/libs/prx/libkernel/File/src/Open.cpp
index 9760bbe879b..8721a364f73 100644
--- a/core/libs/prx/libkernel/File/src/Open.cpp
+++ b/core/libs/prx/libkernel/File/src/Open.cpp
@@ -173,6 +173,11 @@ static int SceIoErrorFromErrno(int error) {
     return static_cast<int>(0x80020000u | static_cast<unsigned>(guest));
 }
 
+static bool InvalidOpenFlags(int flags) {
+    constexpr int createExclusiveDirectory = SCE_KERNEL_O_CREAT | SCE_KERNEL_O_EXCL | SCE_KERNEL_O_DIRECTORY;
+    return (flags & SCE_KERNEL_O_ACCMODE) == SCE_KERNEL_O_ACCMODE || (flags & createExclusiveDirectory) == createExclusiveDirectory;
+}
+
 static int OpenNative(const std::filesystem::path& native, int flags, std::uint16_t mode) {
 #ifdef _WIN32
     if ((flags & (SCE_KERNEL_O_DIRECTORY | SCE_KERNEL_O_CREAT)) == SCE_KERNEL_O_DIRECTORY) {
@@ -211,6 +216,7 @@ static int OpenNative(const std::filesystem::path& native, int flags, std::uint1
 extern "C" {
 
 int APS5_VABI sceKernelOpen(const char* path, int flags, std::uint16_t mode) {
+    if (InvalidOpenFlags(flags)) return SCE_KERNEL_ERROR_EINVAL;
     if (path != nullptr && *path == '\0') return SCE_KERNEL_ERROR_ENOENT;
     APS5_LOG_OUT("path=%s flags=0x%X nativeFlags=0x%X mode=0%o", path, flags, MapFlags(flags), mode);
     if (path != nullptr && File::IsRandomDevicePath(path)) {
@@ -227,6 +233,7 @@ int APS5_VABI sceKernelOpen(const char* path, int flags, std::uint16_t mode) {
 }
 
 int OpenInDirectory_nid_no_patch(int directory, const char* path, int flags, std::uint16_t mode) {
+    if (InvalidOpenFlags(flags)) return SCE_KERNEL_ERROR_EINVAL;
     int error = 0;
     const char* base = GetDirectoryDescriptorPath_nid_no_patch(directory, &error);
     if (base == nullptr) return SceErrorFromErrno(error);
diff --git a/core/libs/tests/GuestFilesystem.cpp b/core/libs/tests/GuestFilesystem.cpp
index b87cf1344c6..796d213c711 100644
--- a/core/libs/tests/GuestFilesystem.cpp
+++ b/core/libs/tests/GuestFilesystem.cpp
@@ -850,6 +850,15 @@ int main() {
     Require(sceKernelOpen(presentName.c_str(), 0x20402, 0) == static_cast<int>(0x80020014u));
     Require(std::filesystem::file_size(present) == 5);
     Require(sceKernelOpen(missingName.c_str(), 0x20000, 0) == static_cast<int>(0x80020002u));
+    const auto invalidFlagsName = (root / "invalid-flags.txt").string();
+    Require(sceKernelOpen(presentName.c_str(), 3, 0) == static_cast<int>(0x80020016u));
+    Require(sceKernelOpen(missingName.c_str(), 0x203, 0600) == static_cast<int>(0x80020016u));
+    Require(open_nid_postfix(presentName.c_str(), 3, 0) == -1 && *__error_nid_postfix() == 22);
+    Require(_open_nid_postfix(presentName.c_str(), 0x403) == -1 && *__error_nid_postfix() == 22);
+    Require(sceKernelOpen(invalidFlagsName.c_str(), 0x20a02, 0600) == static_cast<int>(0x80020016u));
+    Require(open_nid_postfix(invalidFlagsName.c_str(), 0x20a00, 0600) == -1 && *__error_nid_postfix() == 22);
+    Require(!std::filesystem::exists(invalidFlagsName));
+    Require(std::filesystem::file_size(present) == 5);
     Require(open_nid_postfix("", 0, 0) == -1 && *__error_nid_postfix() == 2);
     Require(_open_nid_postfix("", 0) == -1 && *__error_nid_postfix() == 2);
     Require(sceKernelOpen("", 0, 0) == static_cast<int>(0x80020002u));
diff --git a/core/libs/tests/GuestKernelSys.cpp b/core/libs/tests/GuestKernelSys.cpp
index d16ff6789ad..e557b1a1cc9 100644
--- a/core/libs/tests/GuestKernelSys.cpp
+++ b/core/libs/tests/GuestKernelSys.cpp
@@ -323,6 +323,8 @@ int main() {
     Require(sceKernelClose(made) == 0);
     Require(openat_nid_postfix(base, "made.bin", SCE_KERNEL_O_WRONLY | SCE_KERNEL_O_CREAT | SCE_KERNEL_O_EXCL, 0644) == -1 && Error() == 17);
     Require(openat_nid_postfix(base, "missing.bin", SCE_KERNEL_O_RDONLY) == -1 && Error() == 2);
+    Require(openat_nid_postfix(base, "file.txt", SCE_KERNEL_O_ACCMODE) == -1 && Error() == 22);
+    Require(openat_nid_postfix(base, "absent.bin", SCE_KERNEL_O_WRONLY | SCE_KERNEL_O_CREAT | SCE_KERNEL_O_EXCL | SCE_KERNEL_O_DIRECTORY, 0644) == -1 && Error() == 22);
     const auto guestFile = "/" + root.filename().string() + "/file.txt";
     const int absolute = openat_nid_postfix(-1, guestFile.c_str(), SCE_KERNEL_O_RDONLY);
     Require(absolute >= 0 && sceKernelClose(absolute) == 0);