diff --git a/src/flash.c b/src/flash.c
index 89955e9..ee761ba 100644
--- a/src/flash.c
+++ b/src/flash.c
@@ -5,6 +5,8 @@
 
 #include "flash.h"
 
+#include <string.h>
+
 #include <nrfx_nvmc.h>
 #include <nrf_gpio.h>
 #include <nrf_wdt.h>
@@ -17,7 +19,7 @@ static int percent_complete;
 static uint32_t bytes_processed;
 static uint32_t total_bytes;
 
-static void progress(uint32_t nbytes)
+static void progress(int32_t nbytes)
 {
     bytes_processed += nbytes;
 
@@ -28,13 +30,40 @@ static void progress(uint32_t nbytes)
     }
 }
 
+/* slow but no table overhead ;-) */
+uint32_t crc32(const uint8_t *data, uint32_t len)
+{
+	uint32_t crc = 0xffffffff;
+
+	for (int i=0; i<len; i++) {
+		crc = crc ^ data[i];
+		for (int j=0; j<8; j++)
+			crc = (crc >> 1) ^ (0xedb88320 & -(crc & 1));
+	}
+	return ~crc;
+}
+
+static uint32_t check_segment(const struct segment *sg)
+{
+    uint32_t sz = sg->end - sg->start;
+
+    if (sg->crc32 != crc32(sg->data, sz))
+	panic();
+
+    return sz;
+}
+
 static void flash_segment(const struct segment *sg)
 {
     uint32_t pagesz = nrfx_nvmc_flash_page_size_get();
+    uint32_t sz = sg->end - sg->start;
+    int retries = 5;
+
+retry:
     
     /* TODO: Haven't got code to handle the UICR yet */
     if (sg->start >= 0x1000000) {
-	progress(sg->end - sg->start);
+	progress(2 * sz);
 	return;
     }
 
@@ -50,6 +79,17 @@ static void flash_segment(const struct segment *sg)
 		             ((uint32_t *) sg->data)[(addr - sg->start) / 4]);
 	progress(4);
     }
+
+    if (0 != memcmp((void *) sg->start, sg->data, sz)) {
+	progress(-(2 * sz));
+	if (retries--)
+	    goto retry;
+
+	// We're in big trouble... the system is probably bricked but we
+	// don't seem to be able to do anything about it. Better to reboot
+	// and hope than to sit here wearing out the flash!
+	panic();
+    }
 }
 
 void flash_all(void)
@@ -61,7 +101,7 @@ void flash_all(void)
     report_progress(0);
 
     for (int i=0; i<lengthof(segments); i++)
-	total_bytes += 2 * (segments[i].end - segments[i].start);
+	total_bytes += 2 * check_segment(segments + i);
 	
     for (int i=0; i<lengthof(segments); i++)
         flash_segment(segments + i);
diff --git a/src/main.c b/src/main.c
index ffb585f..f603098 100644
--- a/src/main.c
+++ b/src/main.c
@@ -9,8 +9,23 @@
 #include "board.h"
 #include "flash.h"
 #include "st7789.h"
+#include "util.h"
 #include "wdt.h"
 
+void panic(void)
+{
+#ifdef CONFIG_ST7789
+    st7789_state(-1);
+#endif
+    reboot();
+}
+
+void reboot(void)
+{
+    while (true)
+	    /* stop feeding the dog and we'll automatically reboot */;
+}
+
 void report_progress(int percent)
 {
 #ifdef CONFIG_ST7789
@@ -35,9 +50,7 @@ int main()
 #endif
 
     flash_all();
-
-    while (true)
-	    /* stop feeding the dog and we'll automatically reboot */;
+    reboot();
 
     return 0;
 }
diff --git a/src/st7789.c b/src/st7789.c
index b0d7dae..8556afd 100644
--- a/src/st7789.c
+++ b/src/st7789.c
@@ -228,6 +228,13 @@ void st7789_state(int percent_complete)
   const uint16_t bg = 0;
   uint16_t color = bg;
 
+  if (percent_complete < 0)
+      fg = 0xf800;
+  else if (percent_complete < 100)
+      fg = 0x033f;
+  else
+      fg = 0xffff;
+
   for (int i=0; i<sizeof(rle); i++) {
     uint8_t rl = rle[i];
     while (rl) {
@@ -247,7 +254,7 @@ void st7789_state(int percent_complete)
 	if (bottomclip) {
 	  memset(linebuffer+2*(240-64), 0, 64*2);
 	}
-	if (y >= (165-percent_complete)) {
+	if (percent_complete >= 1 && y >= (165-percent_complete)) {
 	  fg = 0xffff;
 	}
 
diff --git a/src/util.h b/src/util.h
index b5dcc64..52f3639 100644
--- a/src/util.h
+++ b/src/util.h
@@ -8,6 +8,8 @@
 
 #define lengthof(x) (sizeof(x) / sizeof((x)[0]))
 
+void panic(void);
+void reboot(void);
 void report_progress(int percent);
 
 #endif /* RELOADER_UTIL_H__ */