diff --git a/Makefile b/Makefile
index b51652a00..3382d9a41 100644
--- a/Makefile
+++ b/Makefile
@@ -62,11 +62,11 @@ pokecrystal.gbc: $(crystal_obj)
 	rgbfix -Cjv -i BYTE -k 01 -l 0x33 -m 0x10 -p 0 -r 3 -t PM_CRYSTAL $@
 
 
-# For files that the compressor can't match, there will be a .lz file suffixed with the hash of the correct uncompressed file.
+# For files that the compressor can't match, there will be a .lz file suffixed with the md5 hash of the correct uncompressed file.
 # If the hash of the uncompressed file matches, use this .lz instead.
 # This allows pngs to be used for compressed graphics and still match.
 
-%.lz: hash = $(shell md5sum $(*D)/$(*F) | sed "s/\(.\{8\}\).*/\1/")
+%.lz: hash = $(shell tools/md5 $(*D)/$(*F) | sed "s/\(.\{8\}\).*/\1/")
 %.lz: %
 	$(eval filename := $@.$(hash))
 	$(if $(wildcard $(filename)),cp $(filename) $@,tools/lzcomp $< $@)
diff --git a/tools/Makefile b/tools/Makefile
index 57a4d84ce..202961c3e 100644
--- a/tools/Makefile
+++ b/tools/Makefile
@@ -9,7 +9,8 @@ all: \
 	palette \
 	pokemon_animation \
 	pokemon_animation_graphics \
-	gfx
+	gfx \
+	md5
 	@:
 
 %: %.c
diff --git a/tools/md5.c b/tools/md5.c
new file mode 100644
index 000000000..9f6473d2c
--- /dev/null
+++ b/tools/md5.c
@@ -0,0 +1,127 @@
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+
+#include "common.h"
+
+static const int s[64] = {
+	7, 12, 17, 22,  7, 12, 17, 22,  7, 12, 17, 22,  7, 12, 17, 22,
+	5,  9, 14, 20,  5,  9, 14, 20,  5,  9, 14, 20,  5,  9, 14, 20,
+	4, 11, 16, 23,  4, 11, 16, 23,  4, 11, 16, 23,  4, 11, 16, 23,
+	6, 10, 15, 21,  6, 10, 15, 21,  6, 10, 15, 21,  6, 10, 15, 21,
+};
+
+static const uint32_t K[64] = {
+	0xd76aa478, 0xe8c7b756, 0x242070db, 0xc1bdceee,
+	0xf57c0faf, 0x4787c62a, 0xa8304613, 0xfd469501,
+	0x698098d8, 0x8b44f7af, 0xffff5bb1, 0x895cd7be,
+	0x6b901122, 0xfd987193, 0xa679438e, 0x49b40821,
+	0xf61e2562, 0xc040b340, 0x265e5a51, 0xe9b6c7aa,
+	0xd62f105d, 0x02441453, 0xd8a1e681, 0xe7d3fbc8,
+	0x21e1cde6, 0xc33707d6, 0xf4d50d87, 0x455a14ed,
+	0xa9e3e905, 0xfcefa3f8, 0x676f02d9, 0x8d2a4c8a,
+	0xfffa3942, 0x8771f681, 0x6d9d6122, 0xfde5380c,
+	0xa4beea44, 0x4bdecfa9, 0xf6bb4b60, 0xbebfbc70,
+	0x289b7ec6, 0xeaa127fa, 0xd4ef3085, 0x04881d05,
+	0xd9d4d039, 0xe6db99e5, 0x1fa27cf8, 0xc4ac5665,
+	0xf4292244, 0x432aff97, 0xab9423a7, 0xfc93a039,
+	0x655b59c3, 0x8f0ccc92, 0xffeff47d, 0x85845dd1,
+	0x6fa87e4f, 0xfe2ce6e0, 0xa3014314, 0x4e0811a1,
+	0xf7537e82, 0xbd3af235, 0x2ad7d2bb, 0xeb86d391,
+};
+
+#define rotate_left_32(value, by) \
+	((((value) << (by)) & 0xffffffff) | ((value) >> 32 - (by)))
+
+void md5_wikipedia(uint8_t *data, int length, uint8_t *result) {
+
+	uint8_t *message = calloc(length + 64, sizeof(uint8_t));
+	memcpy(message, data, length);
+
+	long orig_bitlength = length * 8;
+
+	message[length++] |= 1 << 7;
+
+	while (length % 64 != (64 - 8)) {
+		length++;
+	}
+	for (int i = 0; i < 8; i++) {
+		message[length++] = (orig_bitlength >> (i * 8)) & 0xff;
+	}
+
+	int a0 = 0x67452301;
+	int b0 = 0xefcdab89;
+	int c0 = 0x98badcfe;
+	int d0 = 0x10325476;
+
+	for (int start = 0; start < length; start += 64) {
+		uint32_t M[16];
+		for (int j = 0; j < 16; j++) {
+			uint8_t *word = &message[start + j * 4];
+			M[j] = *word++;
+			M[j] |= *word++ << 8;
+			M[j] |= *word++ << 16;
+			M[j] |= *word++ << 24;
+		}
+
+		int A = a0;
+		int B = b0;
+		int C = c0;
+		int D = d0;
+		for (int i = 0; i < 64; i++) {
+			int F, g;
+			switch (i / 16) {
+			case 0:
+				F = (B & C) | (~B & D);
+				g = i;
+				break;
+			case 1:
+				F = (D & B) | (~D & C);
+				g = (5 * i + 1) % 16;
+				break;
+			case 2:
+				F = B ^ C ^ D;
+				g = (3 * i + 5) % 16;
+				break;
+			case 3:
+				F = C ^ (B | ~D);
+				g = (7 * i) % 16;
+				break;
+			}
+			int e = D;
+			D = C;
+			C = B;
+			B = B + rotate_left_32(A + F + K[i] + M[g], s[i]);
+			A = e;
+		}
+		a0 += A;
+		b0 += B;
+		c0 += C;
+		d0 += D;
+	}
+
+	int values[] = {a0, b0, c0, d0};
+	for (int i = 0; i < 16; i++) {
+		int value = values[i >> 2];
+		int shift = (i % 4) * 8;
+		result[i] = (value >> shift) & 0xff;
+	}
+
+	free(message);
+}
+
+int main(int argc, char *argv[]) {
+	if (argc < 2) {
+		exit(1);
+	}
+	char *infile = argv[1];
+	int size;
+	uint8_t *data = read_u8(infile, &size);
+
+	uint8_t result[16];
+	md5_wikipedia(data, size, result);
+	for (int i = 0; i < 16; i++) {
+		printf("%02x", result[i]);
+	}
+	printf("\n");
+}