diff --git a/wol.c b/wol.c
index e7aa930..9e40089 100644
--- a/wol.c
+++ b/wol.c
@@ -9,20 +9,56 @@
 #include <stdlib.h>
 #include <string.h>
 #include <unistd.h>
-#include <regex.h>
 
-#define MAC_REGEX "^([0-9A-Fa-f]{2}[:-]?){5}([0-9A-Fa-f]{2})$"
+#define MAX_TRIES 10
+
+static int
+xdigit (char c)
+{
+	if (c >= '0' && c <= '9')
+		return (c - '0');
+	else if (c >= 'A' && c <= 'F')
+		return (c - 'A');
+	else if (c >= 'a' && c <= 'f')
+		return (c - 'a');
+	return -1;
+}
+
+static uint8_t *
+ether_str2addr(const char *str, uint8_t *addr)
+{
+	int val0, val1;
+
+	for (int i = 0; i < 6; ++i) {
+		val0 = xdigit(*str);
+		str++;
+		if (val0 < 0)
+			return NULL;
+		val1 = xdigit(*str);
+		str++;
+		if (val1 < 0)
+			return NULL;
+		addr[i] = (uint8_t)((val0 << 4) | val1);
+		if (i < 5 && !isxdigit(*str))
+			str++;
+	}
+	if (*str != '\0')
+		return NULL;
+
+	return addr;
+}
 
 static void
 wake_on_lan(const char *mac_address) {
-	char payload[102];
-	int mac[6];
+	uint8_t payload[102];
+	uint8_t mac[6];
 
-	sscanf(mac_address, "%2x%2x%2x%2x%2x%2x", &mac[0], &mac[1], &mac[2], &mac[3], &mac[4], &mac[5]);
+	if (ether_str2addr(mac_address, mac) == NULL)
+		errx(1, "Invalid MAC address: %s", mac_address);
 
 	memset(payload, 0xFF, 6);
 	for (unsigned int i = 6; i < sizeof(payload); i += 6)
-		memcpy(payload + i, mac, sizeof(mac));
+		memcpy(payload + i, mac, 6);
 
 	struct sockaddr_in sa;
 	memset(&sa, 0, sizeof(sa));
@@ -37,7 +73,7 @@ wake_on_lan(const char *mac_address) {
 	if (setsockopt(sock, SOL_SOCKET, SO_BROADCAST, &(int){1}, sizeof(int)) < 0)
 		err(1, "%s", "setsockopt");
 
-	for (int i = 0; i < 10; ++i)
+	for (int i = 0; i < MAX_TRIES; ++i)
 		if (sendto(sock, payload, sizeof(payload), 0, (struct sockaddr*)&sa, sizeof(sa)) < 0)
 			err(1, "sendto");
 
@@ -51,25 +87,9 @@ main(int argc, char *argv[]) {
 		exit(1);
 	}
 
-	regex_t regex;
-	if (regcomp(&regex, MAC_REGEX, REG_EXTENDED) != 0)
-		errx(1, "%s", "Failed to compile regular expression");
-
-	for (int i = 1; i < argc; ++i) {
-		if (regexec(&regex, argv[i], 0, NULL, 0) != 0)
-			errx(1, "Invalid MAC address: %s", argv[i]);
-
-		char mac_address[13];
-		int k = 0;
-		for (int j = 0; argv[i][j]; ++j)
-			if (isxdigit((int) argv[i][j]))
-				mac_address[k++] = argv[i][j];
-		mac_address[k] = '\0';
-
-		wake_on_lan(mac_address);
-	}
+	for (int i = 1; i < argc; ++i)
+		wake_on_lan(argv[i]);
 
-	regfree(&regex);
 	return (0);
 }