diff --git a/firmware/buffer.c b/firmware/buffer.c
index c3afb5cc4b..180ded8268 100644
--- a/firmware/buffer.c
+++ b/firmware/buffer.c
@@ -20,7 +20,7 @@
 #include "buffer.h"
 
 #ifdef SIMULATOR
-unsigned char mp3buffer[0x200000];
+unsigned char mp3buffer[(MEM*1024-256)*1024];
 unsigned char *mp3end = mp3buffer + sizeof(mp3buffer);
 #else
 /* defined in linker script */
diff --git a/uisimulator/win32/Makefile b/uisimulator/win32/Makefile
index 316f44c900..e7d118cd5a 100644
--- a/uisimulator/win32/Makefile
+++ b/uisimulator/win32/Makefile
@@ -57,7 +57,7 @@ no_configure:
 endif
 
 DEFINES = -DHAVE_CONFIG_H -DGETTIMEOFDAY_TWO_ARGS -DSIMULATOR \
-$(TARGET) -DAPPSVERSION=\"$(VERSION)\" $(EXTRA_DEFINES)
+$(TARGET) -DAPPSVERSION=\"$(VERSION)\" -DMEM=${MEMORYSIZE} $(EXTRA_DEFINES)
 
 LDFLAGS =  -lgdi32 -luser32
 
diff --git a/uisimulator/x11/Makefile b/uisimulator/x11/Makefile
index 3055ca99b5..7b86ee2f5b 100644
--- a/uisimulator/x11/Makefile
+++ b/uisimulator/x11/Makefile
@@ -53,7 +53,7 @@ no_configure:
 endif
 
 DEFINES := -DHAVE_CONFIG_H -DGETTIMEOFDAY_TWO_ARGS -DSIMULATOR \
-$(TARGET) -DAPPSVERSION=\"$(VERSION)\" $(EXTRA_DEFINES) 
+$(TARGET) -DAPPSVERSION=\"$(VERSION)\" -DMEM=${MEMORYSIZE} $(EXTRA_DEFINES) 
 
 # Use this for simulator-only files
 INCLUDES = -I. -I$(EXPORT) -I$(APPSDIR) -I$(MACHINEDIR) -I$(SIMCOMMON) -I$(OBJDIR) -I$(PLUGINDIR)/lib