diff --git a/Core/MIPS/MIPSAnalyst.cpp b/Core/MIPS/MIPSAnalyst.cpp
index 6e88bbf63f..71d1d7c831 100644
--- a/Core/MIPS/MIPSAnalyst.cpp
+++ b/Core/MIPS/MIPSAnalyst.cpp
@@ -983,7 +983,8 @@ skip:
 		// We assume the furthest jumpback is within the func.
 		u32 furthestJumpbackAddr = INVALIDTARGET;
 
-		for (u32 ahead = fromAddr; ahead < fromAddr + MAX_AHEAD_SCAN; ahead += 4) {
+		const u32 scanEnd = fromAddr + Memory::ValidSize(fromAddr, MAX_AHEAD_SCAN);
+		for (u32 ahead = fromAddr; ahead < scanEnd; ahead += 4) {
 			MIPSOpcode aheadOp = Memory::Read_Instruction(ahead, true);
 			u32 target = GetBranchTargetNoRA(ahead, aheadOp);
 			if (target == INVALIDTARGET && ((aheadOp & 0xFC000000) == 0x08000000)) {
diff --git a/Core/MemMap.h b/Core/MemMap.h
index 465802fb32..b9afe2ea35 100644
--- a/Core/MemMap.h
+++ b/Core/MemMap.h
@@ -313,13 +313,13 @@ inline bool IsValidAddress(const u32 address) {
 inline u32 ValidSize(const u32 address, const u32 requested_size) {
 	u32 max_size;
 	if ((address & 0x3E000000) == 0x08000000) {
-		max_size = 0x08000000 + g_MemorySize - (address & 0x3E000000);
+		max_size = 0x08000000 + g_MemorySize - (address & 0x3FFFFFFF);
 	} else if ((address & 0x3F800000) == 0x04000000) {
-		max_size = 0x04800000 - (address & 0x3F800000);
+		max_size = 0x04800000 - (address & 0x3FFFFFFF);
 	} else if ((address & 0xBFFF0000) == 0x00010000) {
-		max_size = 0x00014000 - (address & 0xBFFF0000);
+		max_size = 0x00014000 - (address & 0xBFFFFFFF);
 	} else if ((address & 0x3F000000) >= 0x08000000 && (address & 0x3F000000) < 0x08000000 + g_MemorySize) {
-		max_size = 0x08000000 + g_MemorySize - (address & 0x3F000000);
+		max_size = 0x08000000 + g_MemorySize - (address & 0x3FFFFFFF);
 	} else {
 		max_size = 0;
 	}
diff --git a/Core/System.cpp b/Core/System.cpp
index 96d6ae5f8a..f46eaa915d 100644
--- a/Core/System.cpp
+++ b/Core/System.cpp
@@ -122,7 +122,8 @@ void UpdateUIState(GlobalUIState newState) {
 	// Never leave the EXIT state.
 	if (globalUIState != newState && globalUIState != UISTATE_EXIT) {
 		globalUIState = newState;
-		host->UpdateDisassembly();
+		if (host)
+			host->UpdateDisassembly();
 		const char *state = nullptr;
 		switch (globalUIState) {
 		case UISTATE_EXIT: state = "exit";  break;
diff --git a/Windows/Debugger/Debugger_MemoryDlg.cpp b/Windows/Debugger/Debugger_MemoryDlg.cpp
index 6532c6a6f1..b11c53425f 100644
--- a/Windows/Debugger/Debugger_MemoryDlg.cpp
+++ b/Windows/Debugger/Debugger_MemoryDlg.cpp
@@ -131,9 +131,8 @@ void CMemoryDlg::searchBoxRedraw(std::vector<u32> results) {
 }
 
 
-void CMemoryDlg::NotifyMapLoaded()
-{
-	if (m_hDlg)
+void CMemoryDlg::NotifyMapLoaded() {
+	if (m_hDlg && g_symbolMap)
 		g_symbolMap->FillSymbolListBox(symListHdl, ST_DATA);
 	Update(); 
 }
diff --git a/Windows/EmuThread.cpp b/Windows/EmuThread.cpp
index a0a8a359fa..0e373989c4 100644
--- a/Windows/EmuThread.cpp
+++ b/Windows/EmuThread.cpp
@@ -263,6 +263,9 @@ void MainThreadFunc() {
 			if (!Core_IsActive())
 				UpdateUIState(UISTATE_MENU);
 			Core_Run(g_graphicsContext);
+			if (coreState == CORE_BOOT_ERROR) {
+				break;
+			}
 		}
 	}
 	Core_Stop();
diff --git a/unittest/UnitTest.cpp b/unittest/UnitTest.cpp
index 65447c27f0..1e0310991b 100644
--- a/unittest/UnitTest.cpp
+++ b/unittest/UnitTest.cpp
@@ -567,6 +567,8 @@ static bool TestMemMap() {
 			EXPECT_EQ_HEX(Memory::ValidSize(base, 0x40000001), range.size);
 			EXPECT_EQ_HEX(Memory::ValidSize(base, 0x20000001), range.size);
 			EXPECT_EQ_HEX(Memory::ValidSize(base, 0x10000001), range.size);
+
+			EXPECT_EQ_HEX(Memory::ValidSize(base + range.size - 0x10, 0x20000001), 0x10);
 		}
 	}
 
@@ -607,6 +609,7 @@ TestItem availableTests[] = {
 	TEST_ITEM(ParseLBN),
 	TEST_ITEM(QuickTexHash),
 	TEST_ITEM(CLZ),
+	TEST_ITEM(MemMap),
 	TEST_ITEM(ShaderGenerators),
 };