diff --git a/makefile b/makefile
index 22731329c50..6a8b34a944d 100644
--- a/makefile
+++ b/makefile
@@ -184,6 +184,9 @@ endif
 # uncomment next line to build a debug version
 # DEBUG = 1
 
+# uncomment next line to disable some debug-related hotspots/slowdowns (e.g. for profiling)
+# FASTDEBUG = 1
+
 # uncomment next line to include the internal profiler
 # PROFILER = 1
 
@@ -443,6 +446,9 @@ ifneq ($(BUILD_JPEGLIB),1)
 DEFS += -DUSE_SYSTEM_JPEGLIB
 endif
 
+ifdef FASTDEBUG
+DEFS += -DMAME_DEBUG_FAST
+endif
 
 
 #-------------------------------------------------
diff --git a/src/emu/emucore.h b/src/emu/emucore.h
index 8a5f71c7313..7c5f2343a0e 100644
--- a/src/emu/emucore.h
+++ b/src/emu/emucore.h
@@ -357,7 +357,7 @@ void report_bad_device_cast(const device_t *dev, const std::type_info &src_type,
 template<class _Dest, class _Source>
 inline _Dest downcast(_Source *src)
 {
-#ifdef MAME_DEBUG
+#if defined(MAME_DEBUG) && !defined(MAME_DEBUG_FAST)
 	try {
 		if (dynamic_cast<_Dest>(src) != src)
 		{
@@ -378,7 +378,7 @@ inline _Dest downcast(_Source *src)
 template<class _Dest, class _Source>
 inline _Dest downcast(_Source &src)
 {
-#ifdef MAME_DEBUG
+#if defined(MAME_DEBUG) && !defined(MAME_DEBUG_FAST)
 	try {
 		if (&dynamic_cast<_Dest>(src) != &src)
 		{
diff --git a/src/emu/schedule.c b/src/emu/schedule.c
index cd34a0b7700..5781db2caf9 100644
--- a/src/emu/schedule.c
+++ b/src/emu/schedule.c
@@ -480,7 +480,9 @@ void device_scheduler::timeslice()
 				attoseconds_t delta = target.attoseconds - exec->m_localtime.attoseconds;
 				if (delta < 0 && target.seconds > exec->m_localtime.seconds)
 					delta += ATTOSECONDS_PER_SECOND;
+#ifndef MAME_DEBUG_FAST
 				assert(delta == (target - exec->m_localtime).as_attoseconds());
+#endif
 
 				// if we have enough for at least 1 cycle, do the math
 				if (delta >= exec->m_attoseconds_per_cycle)
diff --git a/src/osd/windows/windows.mak b/src/osd/windows/windows.mak
index 1c3b0b77596..efe4c567b1b 100644
--- a/src/osd/windows/windows.mak
+++ b/src/osd/windows/windows.mak
@@ -144,7 +144,12 @@ endif
 
 # enable basic run-time checks in non-optimized build
 ifeq ($(OPTIMIZE),0)
+ifndef FASTDEBUG
 CCOMFLAGS += /RTC1
+else
+# disable the stack check since it has quite a speed impact
+CCOMFLAGS += /RTCu
+endif
 endif
 
 ifdef MSVC_ANALYSIS