diff --git a/src/drivers/Qt/ConsoleDebugger.cpp b/src/drivers/Qt/ConsoleDebugger.cpp
index db4439e2..111aa93c 100644
--- a/src/drivers/Qt/ConsoleDebugger.cpp
+++ b/src/drivers/Qt/ConsoleDebugger.cpp
@@ -1427,9 +1427,9 @@ void ConsoleDebugger::reloadSymbolsCB(void)
 {
 	fceuWrapperLock();
 	debugSymbolTable.loadGameSymbols();
-	fceuWrapperUnLock();
 
 	asmView->updateAssemblyView();
+	fceuWrapperUnLock();
 }
 //----------------------------------------------------------------------------
 void ConsoleDebugger::debugRunCB(void)
@@ -2812,7 +2812,9 @@ void QAsmView::setDisplayROMoffsets( bool value )
 	{
 		displayROMoffsets = value;
 
+		fceuWrapperLock();
 		updateAssemblyView();
+		fceuWrapperUnLock();
 	}
 }
 //----------------------------------------------------------------------------
@@ -2822,7 +2824,9 @@ void QAsmView::setSymbolDebugEnable( bool value )
 	{
 		symbolicDebugEnable = value;
 
+		fceuWrapperLock();
 		updateAssemblyView();
+		fceuWrapperUnLock();
 	}
 }
 //----------------------------------------------------------------------------
@@ -2832,7 +2836,9 @@ void QAsmView::setRegisterNameEnable( bool value )
 	{
 		registerNameEnable = value;
 
+		fceuWrapperLock();
 		updateAssemblyView();
+		fceuWrapperUnLock();
 	}
 }
 //----------------------------------------------------------------------------
diff --git a/src/drivers/Qt/HexEditor.cpp b/src/drivers/Qt/HexEditor.cpp
index 11a58326..d9663e12 100644
--- a/src/drivers/Qt/HexEditor.cpp
+++ b/src/drivers/Qt/HexEditor.cpp
@@ -41,6 +41,7 @@
 #include "Qt/ConsoleUtilities.h"
 #include "Qt/ConsoleWindow.h"
 
+static bool memNeedsCheck = false;
 static HexBookMarkManager_t hbm;
 static std::list <HexEditorDialog_t*> winList;
 static const char *memViewNames[] = { "RAM", "PPU", "OAM", "ROM", NULL };
@@ -724,7 +725,12 @@ HexEditorDialog_t::HexEditorDialog_t(QWidget *parent)
 
 	periodicTimer->start( 100 ); // 10hz
 
+	// Lock the mutex before adding a new window to the list,
+	// we want to be sure that the emulator is not iterating the list
+	// when we change it.
+	fceuWrapperLock();
 	winList.push_back(this);
+	fceuWrapperUnLock();
 
 	populateBookmarkMenu();
 
@@ -737,6 +743,11 @@ HexEditorDialog_t::~HexEditorDialog_t(void)
 	printf("Hex Editor Deleted\n");
 	periodicTimer->stop();
 
+	// Lock the emulation thread mutex to ensure
+	// that the emulator is not attempting to update memory values
+	// for window while we are destroying it or editing the window list.
+	fceuWrapperLock();
+
 	for (it = winList.begin(); it != winList.end(); it++)
 	{
 		if ( (*it) == this )
@@ -746,6 +757,7 @@ HexEditorDialog_t::~HexEditorDialog_t(void)
 			break;
 		}
 	}
+	fceuWrapperUnLock();
 }
 //----------------------------------------------------------------------------
 void HexEditorDialog_t::setWindowTitle(void)
@@ -1103,7 +1115,18 @@ void HexEditorDialog_t::updatePeriodic(void)
 {
 	//printf("Update Periodic\n");
 
-	editor->checkMemActivity();
+	if ( fceuWrapperTryLock(0) )
+	{
+		memNeedsCheck = false;
+
+		editor->checkMemActivity();
+
+		fceuWrapperUnLock();
+	}
+	else
+	{
+		memNeedsCheck = true;
+	}
 
 	editor->memModeUpdate();
 
@@ -2009,6 +2032,9 @@ void QHexEdit::jumpToROM(void)
 	setAddr( jumpToRomValue );
 }
 //----------------------------------------------------------------------------
+// Calling of checkMemActivity must always be synchronized with the emulation
+// thread as calling GetMem while the emulation is executing can mess up certain
+// registers (especially controller registers $4016 and $4017)
 int QHexEdit::checkMemActivity(void)
 {
 	int c;
@@ -2442,3 +2468,20 @@ int hexEditorOpenFromDebugger( int mode, int addr )
 	return 0;
 }
 //----------------------------------------------------------------------------
+// This function must be called from within the emulation thread
+void hexEditorUpdateMemoryValues(void)
+{
+	std::list <HexEditorDialog_t*>::iterator it;
+
+	if ( !memNeedsCheck )
+	{
+		return;
+	}
+
+	for (it = winList.begin(); it != winList.end(); it++)
+	{
+		(*it)->editor->checkMemActivity();
+	}
+	memNeedsCheck = false;
+}
+//----------------------------------------------------------------------------
diff --git a/src/drivers/Qt/HexEditor.h b/src/drivers/Qt/HexEditor.h
index d0fb5b9d..0ae73b7a 100644
--- a/src/drivers/Qt/HexEditor.h
+++ b/src/drivers/Qt/HexEditor.h
@@ -248,6 +248,7 @@ class HexEditorDialog_t : public QDialog
 };
 
 int hexEditorNumWindows(void);
+void hexEditorUpdateMemoryValues(void);
 void hexEditorLoadBookmarks(void);
 void hexEditorSaveBookmarks(void);
 int hexEditorOpenFromDebugger( int mode, int addr );
diff --git a/src/drivers/Qt/fceuWrapper.cpp b/src/drivers/Qt/fceuWrapper.cpp
index 4ab56df4..e025641a 100644
--- a/src/drivers/Qt/fceuWrapper.cpp
+++ b/src/drivers/Qt/fceuWrapper.cpp
@@ -1043,6 +1043,8 @@ int  fceuWrapperUpdate( void )
 	{
 		DoFun(frameskip, periodic_saves);
 	
+		hexEditorUpdateMemoryValues();
+
 		fceuWrapperUnLock();
 
 		emulatorHasMutux = 0;