diff --git a/NANOVNA_STM32_F303/board.c b/NANOVNA_STM32_F303/board.c
index 6ca71af..677c9b7 100644
--- a/NANOVNA_STM32_F303/board.c
+++ b/NANOVNA_STM32_F303/board.c
@@ -114,11 +114,15 @@ void __early_init(void) {
     bootloader();
     while(1);
    #else
-    __disable_irq();
-    uint32_t foo = SYSCFG->CFGR1;
-    foo = (foo & ~SYSCFG_CFGR1_MEM_MODE) || SYSCFG_CFGR1_MEM_MODE_0;
-    SYSCFG->CFGR1 = foo;
+    // Map the system memory at 0 so interrupts use the bootloader vectors (SYSCFG needs its clock)
+    RCC->APB2ENR |= RCC_APB2ENR_SYSCFGEN;
+    SYSCFG->CFGR1 = (SYSCFG->CFGR1 & ~SYSCFG_CFGR1_MEM_MODE) | SYSCFG_CFGR1_MEM_MODE_0;
     __DSB();
+    __ISB();
+    // The bootloader needs interrupts, crt0 disabled them (as in the F072 board.c)
+    __enable_irq();
+    // and the main stack, crt0 switched to the process stack
+    __set_CONTROL(0);
     __ISB();
 
       __set_MSP(*((uint32_t *)(STM32F303xC_SYSTEM_MEMORY)));
diff --git a/main.c b/main.c
index fe6eb85..97a438e 100644
--- a/main.c
+++ b/main.c
@@ -578,15 +578,14 @@ VNA_SHELL_FUNCTION(cmd_reset)
 {
   (void)argc;
   (void)argv;
-#ifndef TINYSA4
   if (argc == 1) {
     if (get_str_index(argv[0], "dfu") == 0) {
       shell_printf("Performing reset to DFU mode\r\n");
+      chThdSleepMilliseconds(100);        // let USB send the text
       enter_dfu();
       return;
     }
   }
-#endif
   shell_printf("Performing reset\r\n");
   rccEnableWWDG(FALSE);
   WWDG->CFR = 0x60;
diff --git a/ui.c b/ui.c
index 63744a0..979a164 100644
--- a/ui.c
+++ b/ui.c
@@ -750,22 +750,21 @@ extern const char *states[];
   lcd_set_font(FONT_SMALL);
 }
 
-#ifdef __HAS_DFU__
+// Also used by "reset dfu" on the tinySA4, which has no DFU menu (__HAS_DFU__)
 void
 enter_dfu(void)
 {
   int x = 5, y = 5;
   ili9341_set_foreground(LCD_FG_COLOR);
   ili9341_set_background(LCD_BG_COLOR);
-  // leave a last message 
+  // leave a last message
   ili9341_clear_screen();
   ili9341_drawstring_7x13("DFU: Device Firmware Update Mode\n"
                           "To exit DFU mode, please reset device yourself.", x, y);
-  // see __early_init in ./NANOVNA_STM32_F072/board.c
+  // see __early_init in ./NANOVNA_STM32_F072/board.c and ./NANOVNA_STM32_F303/board.c
   *((unsigned long *)BOOT_FROM_SYTEM_MEMORY_MAGIC_ADDRESS) = BOOT_FROM_SYTEM_MEMORY_MAGIC;
   NVIC_SystemReset();
 }
-#endif
 
 static void
 select_lever_mode(int mode)