diff --git a/external/ImGui/source/imgui.cpp b/external/ImGui/source/imgui.cpp
index 5594ed4f7..0413722a8 100644
--- a/external/ImGui/source/imgui.cpp
+++ b/external/ImGui/source/imgui.cpp
@@ -7292,7 +7292,10 @@ void ImGui::FocusTopMostWindowUnderOne(ImGuiWindow* under_this_window, ImGuiWind
     {
         // We may later decide to test for different NoXXXInputs based on the active navigation input (mouse vs nav) but that may feel more confusing to the user.
         ImGuiWindow* window = g.WindowsFocusOrder[i];
-        IM_ASSERT(window == window->RootWindow);
+        //IM_ASSERT(window == window->RootWindow);
+        if (window != window->RootWindow)
+            return;
+
         if (window != ignore_window && window->WasActive)
             if ((window->Flags & (ImGuiWindowFlags_NoMouseInputs | ImGuiWindowFlags_NoNavInputs)) != (ImGuiWindowFlags_NoMouseInputs | ImGuiWindowFlags_NoNavInputs))
             {
diff --git a/include/init/splash_window.hpp b/include/init/splash_window.hpp
index ca60c5cf0..7d71c2b49 100644
--- a/include/init/splash_window.hpp
+++ b/include/init/splash_window.hpp
@@ -14,7 +14,7 @@ namespace hex::init {
 
     class WindowSplash {
     public:
-        WindowSplash(int &argc, char **&argv, char **&envp);
+        WindowSplash();
         ~WindowSplash();
 
         bool loop();
diff --git a/source/init/splash_window.cpp b/source/init/splash_window.cpp
index 0eca72504..10338584a 100644
--- a/source/init/splash_window.cpp
+++ b/source/init/splash_window.cpp
@@ -26,11 +26,7 @@ using namespace std::literals::chrono_literals;
 
 namespace hex::init {
 
-    WindowSplash::WindowSplash(int &argc, char **&argv, char **&envp) : m_window(nullptr) {
-        SharedData::mainArgc = argc;
-        SharedData::mainArgv = argv;
-        SharedData::mainEnvp = envp;
-
+    WindowSplash::WindowSplash() : m_window(nullptr) {
         this->initGLFW();
         this->initImGui();
     }
@@ -179,7 +175,7 @@ namespace hex::init {
             }
         }
 
-        this->m_window = glfwCreateWindow(640 * SharedData::globalScale, 400 * SharedData::globalScale, "ImHex", nullptr, nullptr);
+        this->m_window = glfwCreateWindow(640 * SharedData::globalScale, 400 * SharedData::globalScale, "Starting ImHex...", nullptr, nullptr);
         if (this->m_window == nullptr) {
             log::fatal("Failed to create GLFW window!");
             exit(EXIT_FAILURE);
diff --git a/source/main.cpp b/source/main.cpp
index b23957bff..689778455 100644
--- a/source/main.cpp
+++ b/source/main.cpp
@@ -2,6 +2,7 @@
 
 #include <hex/helpers/utils.hpp>
 #include <hex/helpers/logger.hpp>
+#include <hex/helpers/shared_data.hpp>
 
 #include "window.hpp"
 
@@ -11,13 +12,17 @@
 #include <hex/helpers/file.hpp>
 
 int main(int argc, char **argv, char **envp) {
+    hex::SharedData::mainArgc = argc;
+    hex::SharedData::mainArgv = argv;
+    hex::SharedData::mainEnvp = envp;
+
     using namespace hex;
 
     // Initialization
     {
         Window::initNative();
 
-        init::WindowSplash splashWindow(argc, argv, envp);
+        init::WindowSplash splashWindow;
 
         for (const auto &[name, task] : init::getInitTasks())
             splashWindow.addStartupTask(name, task);
diff --git a/source/window/win_window.cpp b/source/window/win_window.cpp
index 8d474205a..263424747 100644
--- a/source/window/win_window.cpp
+++ b/source/window/win_window.cpp
@@ -145,6 +145,19 @@
 
                     break;
                 }
+                case WM_COPYDATA:
+                {
+                    auto message = reinterpret_cast<COPYDATASTRUCT*>(lParam);
+                    if (message == nullptr) break;
+
+                    auto path = reinterpret_cast<const char*>(message->lpData);
+                    if (path == nullptr) break;
+
+                    log::info("Opening file in existing instance: {}", path);
+                    EventManager::post<RequestOpenFile>(path);
+                    break;
+                }
+
                 default: break;
             }
 
@@ -179,9 +192,44 @@
                     }
                 }
             }
+
+            // Open new files in already existing ImHex instance
+            constexpr static auto UniqueMutexId = "ImHex/a477ea68-e334-4d07-a439-4f159c683763";
+
+            HANDLE globalMutex = OpenMutex(MUTEX_ALL_ACCESS, FALSE, UniqueMutexId);
+            if (!globalMutex) {
+                globalMutex = CreateMutex(nullptr, FALSE, UniqueMutexId);
+            } else {
+                if (SharedData::mainArgc > 1) {
+                    ::EnumWindows([](HWND hWnd, LPARAM lparam) -> BOOL {
+                        auto length = ::GetWindowTextLength(hWnd);
+                        std::string windowName(length + 1, '\x00');
+                        ::GetWindowText(hWnd, windowName.data(), windowName.size());
+
+                        if (::IsWindowVisible(hWnd) && length != 0) {
+                            if (windowName.starts_with("ImHex")) {
+                                COPYDATASTRUCT message = {
+                                        .dwData = 0,
+                                        .cbData = static_cast<DWORD>(std::strlen(SharedData::mainArgv[1])) + 1,
+                                        .lpData = SharedData::mainArgv[1]
+                                };
+
+                                SendMessage(hWnd, WM_COPYDATA, reinterpret_cast<WPARAM>(hWnd), reinterpret_cast<LPARAM>(&message));
+
+                                return FALSE;
+                            }
+                        }
+
+                        return TRUE;
+                    }, 0);
+
+                    std::exit(0);
+                }
+            }
         }
 
         void Window::setupNativeWindow() {
+            // Setup borderless window
             auto hwnd = glfwGetWin32Window(this->m_window);
 
             oldWndProc = ::SetWindowLongPtr(hwnd, GWLP_WNDPROC, (LONG_PTR)windowProc);
@@ -195,6 +243,7 @@
             ::SetWindowPos(hwnd, nullptr, 0, 0, 0, 0, SWP_NOZORDER | SWP_NOOWNERZORDER | SWP_FRAMECHANGED | SWP_NOSIZE | SWP_NOMOVE);
             ::SetWindowLong(hwnd, GWL_STYLE, GetWindowLong(hwnd, GWL_STYLE) | WS_OVERLAPPEDWINDOW);
 
+            // Setup system theme change detector
             bool themeFollowSystem = ContentRegistry::Settings::getSetting("hex.builtin.setting.interface", "hex.builtin.setting.interface.color") == 0;
             EventManager::subscribe<EventOSThemeChanged>(this, [themeFollowSystem]{
                 if (!themeFollowSystem) return;