diff --git a/common/include/err.hpp b/common/include/err.hpp
index 79d2e5e..b0daa9d 100644
--- a/common/include/err.hpp
+++ b/common/include/err.hpp
@@ -6,6 +6,8 @@ enum Err {
     ERR_INVALID_ARGUMENTS,
     ERR_OUT_OF_MEMORY,
     ERR_ALREADY_RUNNING,
+    ERR_CREATE_MUTEX,
+    ERR_MUTEX_TIMEOUT,
     ERR_CREATE_FILE_MAPPING,
     ERR_OPEN_FILE_MAPPING,
     ERR_CREATE_EVENT,
diff --git a/common/include/version.hpp b/common/include/version.hpp
index d7e4c19..a906781 100644
--- a/common/include/version.hpp
+++ b/common/include/version.hpp
@@ -1,6 +1,6 @@
 #ifndef VERSION_HPP
 #define VERSION_HPP
 
-#define VERSION_STRING "0.5.0"
+#define VERSION_STRING "0.5.1"
 
 #endif /* VERSION_HPP */
diff --git a/injector/hook.cpp b/injector/hook.cpp
index 558b795..b040d06 100644
--- a/injector/hook.cpp
+++ b/injector/hook.cpp
@@ -186,7 +186,10 @@ extern "C" __declspec(dllexport) LRESULT CALLBACK IMControl_WndProcHook(int nCod
                             LOG_ERROR("ERROR: GetCompartment(GUID_COMPARTMENT_KEYBOARD_INPUTMODE_CONVERSION) failed with 0x%0lx", hr);
                         }
                         if (SUCCEEDED(hr)) {
-                            DWORD oldMode = varKeyboardInputModeConversion.lVal;
+                            DWORD oldMode = 0;
+                            if (varKeyboardInputModeConversion.vt == VT_I4 || varKeyboardInputModeConversion.vt == VT_UI4) {
+                                oldMode = varKeyboardInputModeConversion.lVal;
+                            }
                             DWORD newMode = oldMode;
                             if  (*g_pSharedData->conversionModeNative) {
                                 newMode |= TF_CONVERSIONMODE_NATIVE;
@@ -194,6 +197,7 @@ extern "C" __declspec(dllexport) LRESULT CALLBACK IMControl_WndProcHook(int nCod
                                 newMode &= ~TF_CONVERSIONMODE_NATIVE;
                             }
                             if (newMode != oldMode) {
+                                varKeyboardInputModeConversion.vt = VT_I4;
                                 varKeyboardInputModeConversion.lVal = newMode;
                                 hr = keyboardInputModeConversionCompartment->SetValue(0, &varKeyboardInputModeConversion);
                             }
diff --git a/main/main.cpp b/main/main.cpp
index 4f3e604..566425e 100644
--- a/main/main.cpp
+++ b/main/main.cpp
@@ -167,7 +167,25 @@ int main(int argc, const char *argv[]) {
 
     logInit("main");
 
-    // Open shared memory for data sharing, and also for ensuring only one instance is running.
+    // Use a named mutex for serialization (auto-released when process dies,
+    // unlike file mapping which can leak when hook DLL remains in target)
+    HANDLE hMutex = CreateMutexA(NULL, FALSE, "Local\\IMControlMutex");
+    if (hMutex == NULL) {
+        eprintln("%s: CreateMutex() failed with 0x%lx.", argv[0], GetLastError());
+        LOG_ERROR("CreateMutex() failed with 0x%lx", GetLastError());
+        err = ERR_CREATE_MUTEX;
+    }
+    if (!err) {
+        DWORD dwMutexResult = WaitForSingleObject(hMutex, 10000);
+        if (dwMutexResult != WAIT_OBJECT_0) {
+            eprintln("%s: Timed out waiting for mutex.", argv[0]);
+            LOG_ERROR("Timed out waiting for mutex");
+            CloseHandle(hMutex);
+            return ERR_MUTEX_TIMEOUT;
+        }
+    }
+
+    // Open shared memory for data sharing (no longer used as singleton guard)
     HANDLE hMapFile = CreateFileMapping(INVALID_HANDLE_VALUE,
                                         NULL,
                                         PAGE_READWRITE,
@@ -179,12 +197,6 @@ int main(int argc, const char *argv[]) {
         LOG_ERROR("CreateFileMapping failed with 0x%lx", GetLastError());
         err = ERR_CREATE_FILE_MAPPING;
     }
-    if (!err) {
-        if (GetLastError() == ERROR_ALREADY_EXISTS) {
-            CloseHandle(hMapFile);
-            return ERR_ALREADY_RUNNING;
-        }
-    }
 
     SharedData* pSharedData = NULL;
     if (!err) {
@@ -203,11 +215,16 @@ int main(int argc, const char *argv[]) {
         }
     }
 
-    HANDLE hEvent = CreateEventA(NULL, TRUE, FALSE, "Local\\IMControlDoneEvent");
-    if (hEvent == NULL) {
-        eprintln("%s: CreateEventA() failed with 0x%lx.", argv[0], GetLastError());
-        LOG_ERROR("CreateEventA() failed with 0x%lx", GetLastError());
-        err = ERR_CREATE_EVENT;
+    HANDLE hEvent = NULL;
+    if (!err) {
+        hEvent = CreateEventA(NULL, TRUE, FALSE, "Local\\IMControlDoneEvent");
+        if (hEvent == NULL) {
+            eprintln("%s: CreateEventA() failed with 0x%lx.", argv[0], GetLastError());
+            LOG_ERROR("CreateEventA() failed with 0x%lx", GetLastError());
+            err = ERR_CREATE_EVENT;
+        } else {
+            ResetEvent(hEvent);
+        }
     }
 
     HWND hForegroundWindow = NULL;
@@ -405,7 +422,7 @@ int main(int argc, const char *argv[]) {
 
     if (!err) {
         LOG_INFO("Waiting for injector to finish...");
-        DWORD dwWaitResult = WaitForSingleObject(hEvent, INFINITE);
+        DWORD dwWaitResult = WaitForSingleObject(hEvent, 10000);
         switch (dwWaitResult) {
             case WAIT_OBJECT_0:
                 LOG_INFO("Injector finished.");
@@ -415,6 +432,11 @@ int main(int argc, const char *argv[]) {
                     LOG_ERROR("injector exited with code %d", err);
                 }
                 break;
+            case WAIT_TIMEOUT:
+                eprintln("%s: Timed out waiting for injector (10s).", argv[0]);
+                LOG_ERROR("Timed out waiting for injector (10s)");
+                err = ERR_SEND_MESSAGE_TIMEOUT_TIMED_OUT;
+                break;
             case WAIT_FAILED:
                 eprintln("%s: WaitForSingleObject() failed with 0x%lx.", argv[0], GetLastError());
                 LOG_ERROR("WaitForSingleObject() failed with 0x%lx", GetLastError());
@@ -470,6 +492,10 @@ int main(int argc, const char *argv[]) {
     if (hMapFile != NULL) {
         CloseHandle(hMapFile);
     }
+    if (hMutex != NULL) {
+        ReleaseMutex(hMutex);
+        CloseHandle(hMutex);
+    }
 
     LOG_INFO("Exiting with code %d", err);