diff --git a/ethermess-backend.c b/ethermess-backend.c
index 8d095e2..2a20341 100644
--- a/ethermess-backend.c
+++ b/ethermess-backend.c
@@ -146,7 +146,6 @@ intmax_t saturating_add(intmax_t a, intmax_t b) {
 		// b < INTMAX_MIN - a
 		if (b < INTMAX_MIN - a) {
 			// Underflow
-			fprintf(stderr, "a+b underflow\n"); // debg
 			return INTMAX_MIN;
 		}
 	} else if (a < 0 && b >= 0) {
@@ -168,7 +167,6 @@ intmax_t saturating_add(intmax_t a, intmax_t b) {
 		// b > INTMAX_MAX - a
 		if (b > INTMAX_MAX - a) {
 			// Overflow
-			fprintf(stderr, "a+b overflow\n"); // debg
 			return INTMAX_MAX;
 		}
 	}
@@ -186,7 +184,6 @@ intmax_t saturating_sub(intmax_t a, intmax_t b) {
 		// a - b + c - c
 		// a - (b - c) - c
 		// a + (c - b) - c
-		fprintf(stderr, "-b overflow\n"); // debg
 		intmax_t c = saturating_sub(b, -INTMAX_MAX);
 		return saturating_sub(saturating_add(a, c - b), c);
 	} else {
@@ -209,7 +206,6 @@ intmax_t saturating_mul(intmax_t a, intmax_t b) {
 
 	if (INTMAX_MAX / a < b) {
 		// Overflow
-		fprintf(stderr, "a*b overflow\n"); // debg
 		return INTMAX_MAX;
 	}
 
@@ -247,21 +243,6 @@ int wait_ms_until(struct timespec then) {
 	return (int)ms;
 }
 
-char hexify(int nybble) {
-	assert(0 <= nybble && nybble <= 16);
-	return "0123456789abcdef"[nybble];
-}
-
-void format_mac(const unsigned char binary_address[6], char formatted[18]) {
-	for (size_t i = 0; i < 6; i++) {
-		unsigned char byte = binary_address[i];
-		formatted[3*i] = hexify(byte >> 4);
-		formatted[3*i + 1] = hexify(byte & 0xf);
-		formatted[3*i + 2] = ':';
-	}
-	formatted[17] = '\0';
-}
-
 void drop_privileges(void) {
 	uid_t uid = getuid();
 	gid_t gid = getgid();
@@ -497,7 +478,7 @@ void read_command(void) {
 	} else if (cmd == 'm') {
 		read_message();
 	} else {
-		fprintf(stderr, "?"); //debg
+		errx(1, "Frontend sent an unknown command %c", cmd);
 	}
 }