diff --git a/ili9341.c b/ili9341.c
index e134025..6372f1c 100644
--- a/ili9341.c
+++ b/ili9341.c
@@ -21,7 +21,7 @@
 #include "hal.h"
 #include "nanovna.h"
 
-uint16_t spi_buffer[2048];
+uint16_t spi_buffer[SPI_BUFFER_SIZE];
 // Default foreground & background colors
 uint16_t foreground_color=DEFAULT_FG_COLOR;
 uint16_t background_color=DEFAULT_BG_COLOR;
diff --git a/nanovna.h b/nanovna.h
index b516545..97522ec 100644
--- a/nanovna.h
+++ b/nanovna.h
@@ -300,6 +300,9 @@ extern int16_t vbat;
 #define RGB565(r,g,b)  ( (((g)&0x1c)<<11) | (((b)&0xf8)<<5) | ((r)&0xf8) | (((g)&0xe0)>>5) )
 #define RGBHEX(hex) ( (((hex)&0x001c00)<<3) | (((hex)&0x0000f8)<<5) | (((hex)&0xf80000)>>16) | (((hex)&0x00e000)>>13) )
 
+// Define size of screen buffer in pixels (one pixel 16bit size)
+#define SPI_BUFFER_SIZE	            2048
+
 #define DEFAULT_FG_COLOR			RGB565(255,255,255)
 #define DEFAULT_BG_COLOR			RGB565(  0,  0,  0)
 #define DEFAULT_GRID_COLOR			RGB565(128,128,128)
@@ -317,7 +320,7 @@ extern int16_t vbat;
 extern uint16_t foreground_color;
 extern uint16_t background_color;
 
-extern uint16_t spi_buffer[2048];
+extern uint16_t spi_buffer[SPI_BUFFER_SIZE];
 
 void ili9341_init(void);
 //void ili9341_setRotation(uint8_t r);
diff --git a/plot.c b/plot.c
index b514311..0e67fbd 100644
--- a/plot.c
+++ b/plot.c
@@ -16,6 +16,10 @@ int16_t area_height = AREA_HEIGHT_NORMAL;
 // Depends from spi_buffer size, CELLWIDTH*CELLHEIGHT <= sizeof(spi_buffer)
 #define CELLWIDTH  (64)
 #define CELLHEIGHT (32)
+// Check buffer size
+#if CELLWIDTH*CELLHEIGHT > SPI_BUFFER_SIZE
+#error "Too small spi_buffer size SPI_BUFFER_SIZE < CELLWIDTH*CELLHEIGH"
+#endif
 
 // indicate dirty cells (not redraw if cell data not changed)
 #define MAX_MARKMAP_X    ((320+CELLWIDTH-1)/CELLWIDTH)