diff --git a/Core/Debugger/DisassemblyManager.cpp b/Core/Debugger/DisassemblyManager.cpp
index 2b75d5dbce..0ba3cc1467 100644
--- a/Core/Debugger/DisassemblyManager.cpp
+++ b/Core/Debugger/DisassemblyManager.cpp
@@ -342,15 +342,20 @@ void DisassemblyManager::clear()
 
 DisassemblyFunction::DisassemblyFunction(u32 _address, u32 _size): address(_address), size(_size)
 {
+	auto memLock = Memory::Lock();
+	if (!PSP_IsInited())
+		return;
+
 	hash = computeHash(address,size);
 	load();
 }
 
 void DisassemblyFunction::recheck()
 {
-	if (!PSP_IsInited()) {
+	auto memLock = Memory::Lock();
+	if (!PSP_IsInited())
 		return;
-	}
+
 	u32 newHash = computeHash(address,size);
 	if (hash != newHash)
 	{
@@ -800,12 +805,20 @@ bool DisassemblyMacro::disassemble(u32 address, DisassemblyLineInfo& dest, bool
 
 DisassemblyData::DisassemblyData(u32 _address, u32 _size, DataType _type): address(_address), size(_size), type(_type)
 {
+	auto memLock = Memory::Lock();
+	if (!PSP_IsInited())
+		return;
+
 	hash = computeHash(address,size);
 	createLines();
 }
 
 void DisassemblyData::recheck()
 {
+	auto memLock = Memory::Lock();
+	if (!PSP_IsInited())
+		return;
+
 	u32 newHash = computeHash(address,size);
 	if (newHash != hash)
 	{
diff --git a/Core/MemMap.cpp b/Core/MemMap.cpp
index ee9c9699fc..6a157fe716 100644
--- a/Core/MemMap.cpp
+++ b/Core/MemMap.cpp
@@ -17,6 +17,7 @@
 
 #include <algorithm>
 
+#include "base/mutex.h"
 #include "Common/Common.h"
 #include "Common/MemoryUtil.h"
 #ifndef __SYMBIAN32__
@@ -89,6 +90,8 @@ u32 g_MemorySize;
 // Used to store the PSP model on game startup.
 u32 g_PSPModel;
 
+recursive_mutex g_shutdownLock;
+
 // We don't declare the IO region in here since its handled by other means.
 static MemoryView views[] =
 {
@@ -370,6 +373,7 @@ void DoState(PointerWrap &p)
 
 void Shutdown()
 {
+	lock_guard guard(g_shutdownLock);
 	u32 flags = 0;
 
 	MemoryMap_Shutdown(flags);
@@ -387,6 +391,21 @@ void Clear()
 		memset(m_pVRAM, 0, VRAM_SIZE);
 }
 
+// Wanting to avoid include pollution, MemMap.h is included a lot.
+MemoryInitedLock::MemoryInitedLock()
+{
+	g_shutdownLock.lock();
+}
+MemoryInitedLock::~MemoryInitedLock()
+{
+	g_shutdownLock.unlock();
+}
+
+MemoryInitedLock Lock()
+{
+	return MemoryInitedLock();
+}
+
 static Opcode Read_Instruction(u32 address, bool resolveReplacements, Opcode inst)
 {
 	if (!MIPS_IS_EMUHACK(inst.encoding)) {
diff --git a/Core/MemMap.h b/Core/MemMap.h
index 07a829be53..d4cbf398b6 100644
--- a/Core/MemMap.h
+++ b/Core/MemMap.h
@@ -126,6 +126,17 @@ void Shutdown();
 void DoState(PointerWrap &p);
 void Clear();
 
+class MemoryInitedLock
+{
+public:
+	MemoryInitedLock();
+	~MemoryInitedLock();
+};
+
+// This doesn't lock memory access or anything, it just makes sure memory isn't freed.
+// Use it when accessing PSP memory from external threads.
+MemoryInitedLock Lock();
+
 // used by JIT to read instructions. Does not resolve replacements.
 Opcode Read_Opcode_JIT(const u32 _Address);
 // used by JIT. Reads in the "Locked cache" mode
diff --git a/Windows/Debugger/CtrlDisAsmView.cpp b/Windows/Debugger/CtrlDisAsmView.cpp
index 61dfd8e221..fc8de5a76d 100644
--- a/Windows/Debugger/CtrlDisAsmView.cpp
+++ b/Windows/Debugger/CtrlDisAsmView.cpp
@@ -203,6 +203,10 @@ COLORREF scaleColor(COLORREF color, float factor)
 
 bool CtrlDisAsmView::getDisasmAddressText(u32 address, char* dest, bool abbreviateLabels, bool showData)
 {
+	auto memLock = Memory::Lock();
+	if (!PSP_IsInited())
+		return false;
+
 	if (displaySymbols)
 	{
 		const std::string addressSymbol = symbolMap.GetLabelString(address);
@@ -256,6 +260,7 @@ void CtrlDisAsmView::assembleOpcode(u32 address, std::string defaultText)
 {
 	u32 encoded;
 
+	auto memLock = Memory::Lock();
 	if (Core_IsStepping() == false) {
 		MessageBox(wnd,L"Cannot change code while the core is running!",L"Error",MB_OK);
 		return;
@@ -1085,6 +1090,10 @@ void CtrlDisAsmView::onMouseMove(WPARAM wParam, LPARAM lParam, int button)
 
 void CtrlDisAsmView::updateStatusBarText()
 {
+	auto memLock = Memory::Lock();
+	if (!PSP_IsInited())
+		return;
+
 	char text[512];
 	DisassemblyLineInfo line;
 	manager.getLine(curAddress,true,line);
diff --git a/Windows/Debugger/CtrlMemView.cpp b/Windows/Debugger/CtrlMemView.cpp
index 8de363dc6d..d7e1ea5311 100644
--- a/Windows/Debugger/CtrlMemView.cpp
+++ b/Windows/Debugger/CtrlMemView.cpp
@@ -362,6 +362,10 @@ void CtrlMemView::onKeyDown(WPARAM wParam, LPARAM lParam)
 
 void CtrlMemView::onChar(WPARAM wParam, LPARAM lParam)
 {
+	auto memLock = Memory::Lock();
+	if (!PSP_IsInited())
+		return;
+
 	if (KeyDownAsync(VK_CONTROL) || wParam == VK_TAB) return;
 
 	if (!Memory::IsValidAddress(curAddress))
@@ -602,6 +606,10 @@ void CtrlMemView::scrollCursor(int bytes)
 
 void CtrlMemView::search(bool continueSearch)
 {
+	auto memLock = Memory::Lock();
+	if (!PSP_IsInited())
+		return;
+
 	u32 searchAddress;
 	if (continueSearch == false || searchQuery[0] == 0)
 	{
diff --git a/Windows/Debugger/DumpMemoryWindow.cpp b/Windows/Debugger/DumpMemoryWindow.cpp
index c5b1035a05..58f6adbca1 100644
--- a/Windows/Debugger/DumpMemoryWindow.cpp
+++ b/Windows/Debugger/DumpMemoryWindow.cpp
@@ -69,6 +69,10 @@ INT_PTR CALLBACK DumpMemoryWindow::dlgFunc(HWND hwnd, UINT iMsg, WPARAM wParam,
 		case IDOK:
 			if (bp->fetchDialogData(hwnd))
 			{
+				auto memLock = Memory::Lock();
+				if (!PSP_IsInited())
+					break;
+
 				FILE* output = fopen(bp->fileName,"wb");
 				if (output == NULL)
 				{
diff --git a/Windows/GEDebugger/GEDebugger.cpp b/Windows/GEDebugger/GEDebugger.cpp
index 828f32a297..662ac02b4f 100644
--- a/Windows/GEDebugger/GEDebugger.cpp
+++ b/Windows/GEDebugger/GEDebugger.cpp
@@ -152,6 +152,11 @@ void CGEDebugger::SetupPreviews() {
 }
 
 void CGEDebugger::UpdatePreviews() {
+	auto memLock = Memory::Lock();
+	if (!PSP_IsInited()) {
+		return;
+	}
+
 	wchar_t desc[256];
 	const GPUDebugBuffer *primaryBuffer = NULL;
 	bool bufferResult = false;
diff --git a/Windows/GEDebugger/TabVertices.cpp b/Windows/GEDebugger/TabVertices.cpp
index 38c14b68bd..7b66a2ecf6 100644
--- a/Windows/GEDebugger/TabVertices.cpp
+++ b/Windows/GEDebugger/TabVertices.cpp
@@ -16,6 +16,7 @@
 // https://github.com/hrydgard/ppsspp and http://www.ppsspp.org/.
 
 #include "base/basictypes.h"
+#include "Core/System.h"
 #include "Windows/resource.h"
 #include "Windows/GEDebugger/GEDebugger.h"
 #include "Windows/GEDebugger/TabVertices.h"
@@ -175,6 +176,12 @@ void CtrlVertexList::FormatVertCol(wchar_t *dest, const GPUDebugVertex &vert, in
 }
 
 void CtrlVertexList::FormatVertColRaw(wchar_t *dest, int row, int col) {
+	auto memLock = Memory::Lock();
+	if (!PSP_IsInited()) {
+		wcscpy(dest, L"Invalid");
+		return;
+	}
+
 	// We could use the vertex decoder and reader, but those already do some minor adjustments.
 	// There's only a few values - let's just go after them directly.
 	const u8 *vert = Memory::GetPointer(gpuDebug->GetVertexAddress()) + row * decoder->size;
@@ -255,6 +262,11 @@ void CtrlVertexList::FormatVertColRawColor(wchar_t *dest, const void *data, int
 }
 
 int CtrlVertexList::GetRowCount() {
+	auto memLock = Memory::Lock();
+	if (!PSP_IsInited()) {
+		return 0;
+	}
+
 	if (!gpuDebug || !Memory::IsValidAddress(gpuDebug->GetVertexAddress())) {
 		rowCount_ = 0;
 		return rowCount_;