diff --git a/Source/Core/Core/IOS/Device.h b/Source/Core/Core/IOS/Device.h
index 64d14adf3f..d393dcd239 100644
--- a/Source/Core/Core/IOS/Device.h
+++ b/Source/Core/Core/IOS/Device.h
@@ -29,6 +29,7 @@ enum ReturnCode : s32
   IPC_EMAX = -5,           // Too many file descriptors open
   IPC_ENOENT = -6,         // File not found
   IPC_EQUEUEFULL = -8,     // Queue full
+  IPC_UNKNOWN = -9,        // Unknown
   IPC_EIO = -12,           // ECC error
   IPC_ENOMEM = -22,        // Alloc failed during request
   FS_EINVAL = -101,        // Invalid path
diff --git a/Source/Core/Core/IOS/STM/STM.cpp b/Source/Core/Core/IOS/STM/STM.cpp
index 0b0e1bbbda..06571b4ae3 100644
--- a/Source/Core/Core/IOS/STM/STM.cpp
+++ b/Source/Core/Core/IOS/STM/STM.cpp
@@ -58,8 +58,20 @@ std::optional<IPCReply> STMImmediateDevice::IOCtl(const IOCtlRequest& request)
     INFO_LOG_FMT(IOS_STM, "    IOCTL_STM_LEDMODE");
     break;
 
+  case IOCTL_STM_HOTRESET_FOR_PD:
+  case IOCTL_STM_WAKEUP:
+  case IOCTL_STM_GET_IDLEMODE:
+  case IOCTL_STM_READDDRREG:
+  case IOCTL_STM_READDDRREG2:
+  case IOCTL_STM_LEDFLASH:
+  case IOCTL_STM_READVER:
+    ERROR_LOG_FMT(IOS_STM, "{} - Unimplemented IOCtl: {}", GetDeviceName(), request.request);
+    break;
+
   default:
     request.DumpUnknown(GetSystem(), GetDeviceName(), Common::Log::LogType::IOS_STM);
+    return_value = IPC_UNKNOWN;
+    break;
   }
 
   return IPCReply(return_value);
@@ -73,7 +85,7 @@ STMEventHookDevice::~STMEventHookDevice()
 std::optional<IPCReply> STMEventHookDevice::IOCtl(const IOCtlRequest& request)
 {
   if (request.request != IOCTL_STM_EVENTHOOK)
-    return IPCReply(IPC_EINVAL);
+    return IPCReply(IPC_UNKNOWN);
 
   if (s_event_hook_request)
     return IPCReply(IPC_EEXIST);
diff --git a/Source/Core/Core/IOS/STM/STM.h b/Source/Core/Core/IOS/STM/STM.h
index e5eb750cd8..ae2068b792 100644
--- a/Source/Core/Core/IOS/STM/STM.h
+++ b/Source/Core/Core/IOS/STM/STM.h
@@ -15,20 +15,23 @@ namespace IOS::HLE
 {
 enum
 {
+  // /dev/stm/eventhook
   IOCTL_STM_EVENTHOOK = 0x1000,
-  IOCTL_STM_GET_IDLEMODE = 0x3001,
-  IOCTL_STM_RELEASE_EH = 0x3002,
+
+  // /dev/stm/immediate
   IOCTL_STM_HOTRESET = 0x2001,
   IOCTL_STM_HOTRESET_FOR_PD = 0x2002,
   IOCTL_STM_SHUTDOWN = 0x2003,
   IOCTL_STM_IDLE = 0x2004,
   IOCTL_STM_WAKEUP = 0x2005,
+  IOCTL_STM_GET_IDLEMODE = 0x3001,
+  IOCTL_STM_RELEASE_EH = 0x3002,
+  IOCTL_STM_READDDRREG = 0x4001,
+  IOCTL_STM_READDDRREG2 = 0x4002,
   IOCTL_STM_VIDIMMING = 0x5001,
   IOCTL_STM_LEDFLASH = 0x6001,
   IOCTL_STM_LEDMODE = 0x6002,
   IOCTL_STM_READVER = 0x7001,
-  IOCTL_STM_READDDRREG = 0x4001,
-  IOCTL_STM_READDDRREG2 = 0x4002,
 };
 
 enum