diff --git a/jni/bootimgtools/hexpatch.c b/jni/bootimgtools/hexpatch.c
index 588e524cb..e48e84c97 100644
--- a/jni/bootimgtools/hexpatch.c
+++ b/jni/bootimgtools/hexpatch.c
@@ -6,6 +6,7 @@
 #include <fcntl.h>
 #include <stdlib.h>
 #include <string.h>
+#include <sys/mman.h>
 
 #include "bootimg.h"
 
@@ -17,13 +18,13 @@ static int hex2int(char c) {
 	return result;
 }
 
-static int hex2ascii(char c, char d) {
+static unsigned hex2ascii(char c, char d) {
 	int high = hex2int(c) * 16;
 	int low = hex2int(d);
-	return high+low;
+	return high + low;
 }
 
-static void hexstr2str(char *hex, char *str) {
+static void hexstr2str(char *hex, unsigned char *str) {
 	char buf = 0;
 	for(int i = 0, length = strlen(hex); i < length; ++i){
 		if(i % 2){
@@ -36,29 +37,23 @@ static void hexstr2str(char *hex, char *str) {
 
 int hexpatch(char * image, char *from, char *to) {
 	int fd = open(image, O_RDWR), patternsize = strlen(from) / 2, patchsize = strlen(to) / 2;
-	off_t filesize = lseek(fd, 0, SEEK_END);
-	char *file, *pattern, *patch, *start;
-	file = malloc(sizeof (char) * filesize);
-	pattern = malloc(sizeof (char) * patternsize);
-	patch = malloc(sizeof (char) * patchsize);
+	size_t filesize = lseek(fd, 0, SEEK_END);
 	lseek(fd, 0, SEEK_SET);
-	read(fd, file, filesize);
+	unsigned char *file, *pattern, *patch;
+	file = mmap(NULL, filesize, PROT_READ | PROT_WRITE, MAP_SHARED, fd, 0);
+	pattern = malloc(patternsize);
+	patch = malloc(patchsize);
 	hexstr2str(from, pattern);
 	hexstr2str(to, patch);
-	for (off_t i = 0; i < filesize;) {
-		int j;
-		for (j = 0; j < patternsize; ++j) {
-			if(file[i + j] != pattern[j]) break;
+	for (size_t i = 0; i < filesize - patternsize; ++i) {
+		if (memcmp(file + i, pattern, patternsize) == 0) {
+			printf("Pattern %s found!\nPatching to %s\n", from, to);
+			memset(file + i, 0, patternsize);
+			memcpy(file + i, patch, patchsize);
+			i += patternsize - 1;
 		}
-		if (j == patternsize) {
-			fprintf(stderr, "Pattern %s found!\nPatching to %s\n", from, to);
-			lseek(fd, i, SEEK_SET);
-			write(fd, patch, patchsize);
-		}
-		if(j == 0) j = 1;
-		i += j;
 	}
-	free(file);
+	munmap(file, filesize);
 	free(pattern);
 	free(patch);
 	close(fd);