diff --git a/stm-firmware/main.c b/stm-firmware/main.c
index f9066d4..4d8a0b2 100644
--- a/stm-firmware/main.c
+++ b/stm-firmware/main.c
@@ -26,6 +26,7 @@
 #include <stdlib.h>
 #include <stdio.h>
 #include <string.h>
+#include <inttypes.h>
 /* #include <arm_math.h> */
 #include <stm32/stm32f4xx.h>
 #include <cmsis/core_cm4.h>
@@ -216,7 +217,7 @@ int main()
 
 
 		rot = rotary_encoder_get_abs_val();
-		snprintf(&disp[0][0], 21U, "Rot-Enc: %u", rot);
+		snprintf(&disp[0][0], 21U, "Rot-Enc: %" PRIu32, rot);
 		strcpy(&disp[1][0], "Line 2");
 		strcpy(&disp[3][0], "Shimatta Reflow");