diff --git a/Core/HLE/sceKernelThread.cpp b/Core/HLE/sceKernelThread.cpp
index 3a19953083..4fcd1545e5 100644
--- a/Core/HLE/sceKernelThread.cpp
+++ b/Core/HLE/sceKernelThread.cpp
@@ -2969,7 +2969,7 @@ void ActionAfterMipsCall::run(MipsCall &call) {
 
 ActionAfterMipsCall *Thread::getRunningCallbackAction()
 {
-	if (this->GetUID() == currentThread && g_inCbCount > 0) 	{
+	if (this->GetUID() == currentThread && g_inCbCount > 0) {
 		MipsCall *call = mipsCalls.get(this->currentMipscallId);
 		ActionAfterMipsCall *action = 0;
 		if (call)
diff --git a/Core/HLE/sceUmd.cpp b/Core/HLE/sceUmd.cpp
index 27da50810b..fe4448b809 100644
--- a/Core/HLE/sceUmd.cpp
+++ b/Core/HLE/sceUmd.cpp
@@ -114,7 +114,8 @@ void __UmdStatChange(u64 userdata, int cyclesLate)
 void __KernelUmdActivate()
 {
 	u32 notifyArg = PSP_UMD_PRESENT | PSP_UMD_READABLE;
-	__KernelNotifyCallback(driveCBId, notifyArg);
+	if (driveCBId != -1)
+		__KernelNotifyCallback(driveCBId, notifyArg);
 
 	// Don't activate immediately, take time to "spin up."
 	CoreTiming::RemoveAllEvents(umdStatChangeEvent);
@@ -124,7 +125,8 @@ void __KernelUmdActivate()
 void __KernelUmdDeactivate()
 {
 	u32 notifyArg = PSP_UMD_PRESENT | PSP_UMD_READY;
-	__KernelNotifyCallback(driveCBId, notifyArg);
+	if (driveCBId != -1)
+		__KernelNotifyCallback(driveCBId, notifyArg);
 
 	CoreTiming::RemoveAllEvents(umdStatChangeEvent);
 	__UmdStatChange(0, 0);
@@ -256,7 +258,7 @@ int sceUmdDeactivate(u32 mode, const char *name)
 
 u32 sceUmdRegisterUMDCallBack(u32 cbId)
 {
-	int retVal;
+	int retVal = 0;
 
 	// TODO: If the callback is invalid, return PSP_ERROR_UMD_INVALID_PARAM.
 	if (!kernelObjects.IsValid(cbId)) {