diff --git a/rom-patcher-js/modules/RomPatcher.format.bps.js b/rom-patcher-js/modules/RomPatcher.format.bps.js
index ca8a4a3..b2e8266 100644
--- a/rom-patcher-js/modules/RomPatcher.format.bps.js
+++ b/rom-patcher-js/modules/RomPatcher.format.bps.js
@@ -26,6 +26,10 @@ BPS.prototype.toString=function(){
 	s+='\n#Actions: '+this.actions.length;
 	return s
 }
+BPS.prototype.calculateFileChecksum = function () {
+	var patchFile = this.export();
+	return patchFile.hashCRC32(0, patchFile.fileSize - 4);
+}
 BPS.prototype.validateSource=function(romFile,headerSize){return this.sourceChecksum===romFile.hashCRC32(headerSize)}
 BPS.prototype.getValidationInfo=function(){
 	return {
@@ -121,7 +125,7 @@ BPS.fromFile=function(file){
 	patch.targetChecksum=file.readU32();
 	patch.patchChecksum=file.readU32();
 
-	if(patch.patchChecksum!==file.hashCRC32(0, file.fileSize - 4)){
+	if (patch.patchChecksum !== patch.calculateFileChecksum()) {
 		throw new Error('Patch checksum mismatch');
 	}
 
@@ -240,8 +244,7 @@ BPS.buildFromRoms=function(original, modified, deltaMode){
 
 	patch.sourceChecksum=original.hashCRC32();
 	patch.targetChecksum=modified.hashCRC32();
-	var patchFile=patch.export();
-	patch.patchChecksum=patchFile.hashCRC32(0, patchFile.fileSize - 4);
+	patch.patchChecksum = patch.calculateFileChecksum();
 	return patch;
 }
 
diff --git a/test.js b/test.js
index f6442ea..0d2d8d8 100644
--- a/test.js
+++ b/test.js
@@ -114,11 +114,11 @@ const TEST_DATA = (new Uint8Array([
 _test('HashCalculator integrity', function () {
 	if (HashCalculator.md5(TEST_DATA) !== '55c76e7e683fd7cd63c673c5df3efa6e')
 		throw new Error('invalid MD5');
-	if (HashCalculator.crc32(TEST_DATA).toString(16) !== '903a031b')
+	if (HashCalculator.crc32(TEST_DATA) !== 0x903a031b)
 		throw new Error('invalid CRC32');
-	if (HashCalculator.adler32(TEST_DATA).toString(16) !== 'ef984205')
+	if (HashCalculator.adler32(TEST_DATA) !== 0xef984205)
 		throw new Error('invalid ADLER32');
-	if (HashCalculator.crc16(TEST_DATA).toString(16) !== '96e4')
+	if (HashCalculator.crc16(TEST_DATA) !== 0x96e4)
 		throw new Error('invalid SHA1');
 });
 
@@ -134,11 +134,9 @@ const MODIFIED_TEST_DATA = (new Uint8Array([
 		const patchedFile = RomPatcher.applyPatch(originalFile, patch, { requireValidation: true });
 
 		if (patchFormat === 'bps') {
-			const patchFile = patch.export();
-			const patchChecksum = patchFile.hashCRC32(0, patchFile.fileSize - 4);
-			if (patch.patchChecksum !== patchChecksum)
+			if (patch.patchChecksum !== patch.calculateFileChecksum())
 				throw new Error('invalid patch checksum');
-			else if (patchFile.hashCRC32() !== 0x2144df1c)
+			else if (patch.export().hashCRC32() !== 0x2144df1c)
 				throw new Error('invalid BPS crc32');
 		}