diff --git a/Makefile b/Makefile
index 57dc6f8..26ef692 100644
--- a/Makefile
+++ b/Makefile
@@ -12,6 +12,7 @@ DEPS=$(sort $(wildcard bits/*.js))
 TARGET=$(LIB).js
 FLOWTARGET=$(LIB).flow.js
 FLOWTGTS=$(TARGET) $(AUXTARGETS)
+CLOSURE=/usr/local/lib/node_modules/google-closure-compiler/compiler.jar
 
 ## Main Targets
 
@@ -86,6 +87,7 @@ lint: $(TARGET) $(AUXTARGETS) ## Run jshint and jscs checks
 	@jshint --show-non-errors package.json
 	@jshint --show-non-errors --extract=always $(HTMLLINT)
 	@jscs $(TARGET) $(AUXTARGETS)
+	if [ -e $(CLOSURE) ]; then java -jar $(CLOSURE) $(REQS) $(FLOWTARGET) --jscomp_warning=reportUnknownTypes >/dev/null; fi
 
 .PHONY: flow
 flow: lint ## Run flow checker
diff --git a/bits/08_blob.js b/bits/08_blob.js
index 6bf3c06..65aac31 100644
--- a/bits/08_blob.js
+++ b/bits/08_blob.js
@@ -69,7 +69,7 @@ function ReadShift(size/*:number*/, t/*:?any*/) {
 
 function CheckField(hexstr/*:string*/, fld/*:string*/) {
 	var m = __hexlify(this,this.l,hexstr.length>>1);
-	if(m !== hexstr) throw fld + 'Expected ' + hexstr + ' saw ' + m;
+	if(m !== hexstr) throw new Error(fld + 'Expected ' + hexstr + ' saw ' + m);
 	this.l += hexstr.length>>1;
 }
 
diff --git a/bits/31_version.js b/bits/31_version.js
index 07abf30..2b00ec2 100644
--- a/bits/31_version.js
+++ b/bits/31_version.js
@@ -1 +1 @@
-exports.version = '0.11.0';
+exports.version = '0.11.1';
diff --git a/bits/40_parse.js b/bits/40_parse.js
index 2b0d9fe..09e33dd 100644
--- a/bits/40_parse.js
+++ b/bits/40_parse.js
@@ -18,7 +18,7 @@ var mv = check_get_mver(blob);
 mver = mv[0];
 switch(mver) {
 	case 3: ssz = 512; break; case 4: ssz = 4096; break;
-	default: throw "Major Version: Expected 3 or 4 saw " + mver;
+	default: throw new Error("Major Version: Expected 3 or 4 saw " + mver);
 }
 
 /* reprocess header */
@@ -30,7 +30,7 @@ check_shifts(blob, mver);
 
 // Number of Directory Sectors
 var nds = blob.read_shift(4, 'i');
-if(mver === 3 && nds !== 0) throw '# Directory Sectors: Expected 0 saw ' + nds;
+if(mver === 3 && nds !== 0) throw new Error('# Directory Sectors: Expected 0 saw ' + nds);
 
 // Number of FAT Sectors
 //var nfs = blob.read_shift(4, 'i');
diff --git a/bits/41_mver.js b/bits/41_mver.js
index b5db2ea..75193f7 100644
--- a/bits/41_mver.js
+++ b/bits/41_mver.js
@@ -15,13 +15,14 @@ function check_shifts(blob, mver) {
 	var shift = 0x09;
 
 	// Byte Order
-	blob.chk('feff', 'Byte Order: ');
+	//blob.chk('feff', 'Byte Order: '); // note: some writers put 0xffff
+	blob.l += 2;
 
 	// Sector Shift
 	switch((shift = blob.read_shift(2))) {
-		case 0x09: if(mver !== 3) throw 'MajorVersion/SectorShift Mismatch'; break;
-		case 0x0c: if(mver !== 4) throw 'MajorVersion/SectorShift Mismatch'; break;
-		default: throw 'Sector Shift: Expected 9 or 12 saw ' + shift;
+		case 0x09: if(mver != 3) throw new Error('Sector Shift: Expected 9 saw ' + shift); break;
+		case 0x0c: if(mver != 4) throw new Error('Sector Shift: Expected 12 saw ' + shift); break;
+		default: throw new Error('Sector Shift: Expected 9 or 12 saw ' + shift);
 	}
 
 	// Mini Sector Shift
diff --git a/bits/45_readfat.js b/bits/45_readfat.js
index 37aead4..0ece1a2 100644
--- a/bits/45_readfat.js
+++ b/bits/45_readfat.js
@@ -3,7 +3,7 @@
 function sleuth_fat(idx, cnt, sectors, ssz, fat_addrs) {
 	var q;
 	if(idx === ENDOFCHAIN) {
-		if(cnt !== 0) throw "DIFAT chain shorter than expected";
+		if(cnt !== 0) throw new Error("DIFAT chain shorter than expected");
 	} else if(idx !== -1 /*FREESECT*/) {
 		var sector = sectors[idx], m = (ssz>>>2)-1;
 		if(!sector) return;
@@ -29,7 +29,7 @@ function get_sector_list(sectors, start, fat_addrs, ssz, chkd) {
 		buf_chain.push(sectors[j]);
 		var addr = fat_addrs[Math.floor(j*4/ssz)];
 		jj = ((j*4) & modulus);
-		if(ssz < 4 + jj) throw "FAT boundary crossed: " + j + " 4 "+ssz;
+		if(ssz < 4 + jj) throw new Error("FAT boundary crossed: " + j + " 4 "+ssz);
 		if(!sectors[addr]) break;
 		j = __readInt32LE(sectors[addr], jj);
 	}
@@ -52,7 +52,7 @@ function make_sector_list(sectors, dir_start, fat_addrs, ssz/*:number*/)/*:any*/
 			buf_chain.push(sectors[j]);
 			var addr = fat_addrs[Math.floor(j*4/ssz)];
 			jj = ((j*4) & modulus);
-			if(ssz < 4 + jj) throw "FAT boundary crossed: " + j + " 4 "+ssz;
+			if(ssz < 4 + jj) throw new Error("FAT boundary crossed: " + j + " 4 "+ssz);
 			if(!sectors[addr]) break;
 			j = __readInt32LE(sectors[addr], jj);
 		}
diff --git a/cfb.flow.js b/cfb.flow.js
index 7adaffe..0998b22 100644
--- a/cfb.flow.js
+++ b/cfb.flow.js
@@ -73,7 +73,7 @@ function ReadShift(size/*:number*/, t/*:?any*/) {
 
 function CheckField(hexstr/*:string*/, fld/*:string*/) {
 	var m = __hexlify(this,this.l,hexstr.length>>1);
-	if(m !== hexstr) throw fld + 'Expected ' + hexstr + ' saw ' + m;
+	if(m !== hexstr) throw new Error(fld + 'Expected ' + hexstr + ' saw ' + m);
 	this.l += hexstr.length>>1;
 }
 
@@ -96,7 +96,7 @@ type SectorList = {
 /* [MS-CFB] v20130118 */
 var CFB = (function _CFB(){
 var exports = {};
-exports.version = '0.11.0';
+exports.version = '0.11.1';
 function parse(file) {
 var mver = 3; // major version
 var ssz = 512; // sector size
@@ -117,7 +117,7 @@ var mv = check_get_mver(blob);
 mver = mv[0];
 switch(mver) {
 	case 3: ssz = 512; break; case 4: ssz = 4096; break;
-	default: throw "Major Version: Expected 3 or 4 saw " + mver;
+	default: throw new Error("Major Version: Expected 3 or 4 saw " + mver);
 }
 
 /* reprocess header */
@@ -129,7 +129,7 @@ check_shifts(blob, mver);
 
 // Number of Directory Sectors
 var nds = blob.read_shift(4, 'i');
-if(mver === 3 && nds !== 0) throw '# Directory Sectors: Expected 0 saw ' + nds;
+if(mver === 3 && nds !== 0) throw new Error('# Directory Sectors: Expected 0 saw ' + nds);
 
 // Number of FAT Sectors
 //var nfs = blob.read_shift(4, 'i');
@@ -215,13 +215,14 @@ function check_shifts(blob, mver) {
 	var shift = 0x09;
 
 	// Byte Order
-	blob.chk('feff', 'Byte Order: ');
+	//blob.chk('feff', 'Byte Order: '); // note: some writers put 0xffff
+	blob.l += 2;
 
 	// Sector Shift
 	switch((shift = blob.read_shift(2))) {
-		case 0x09: if(mver !== 3) throw 'MajorVersion/SectorShift Mismatch'; break;
-		case 0x0c: if(mver !== 4) throw 'MajorVersion/SectorShift Mismatch'; break;
-		default: throw 'Sector Shift: Expected 9 or 12 saw ' + shift;
+		case 0x09: if(mver != 3) throw new Error('Sector Shift: Expected 9 saw ' + shift); break;
+		case 0x0c: if(mver != 4) throw new Error('Sector Shift: Expected 12 saw ' + shift); break;
+		default: throw new Error('Sector Shift: Expected 9 or 12 saw ' + shift);
 	}
 
 	// Mini Sector Shift
@@ -303,7 +304,7 @@ function make_find_path(FullPaths, Paths, FileIndex, files, root_name) {
 function sleuth_fat(idx, cnt, sectors, ssz, fat_addrs) {
 	var q;
 	if(idx === ENDOFCHAIN) {
-		if(cnt !== 0) throw "DIFAT chain shorter than expected";
+		if(cnt !== 0) throw new Error("DIFAT chain shorter than expected");
 	} else if(idx !== -1 /*FREESECT*/) {
 		var sector = sectors[idx], m = (ssz>>>2)-1;
 		if(!sector) return;
@@ -329,7 +330,7 @@ function get_sector_list(sectors, start, fat_addrs, ssz, chkd) {
 		buf_chain.push(sectors[j]);
 		var addr = fat_addrs[Math.floor(j*4/ssz)];
 		jj = ((j*4) & modulus);
-		if(ssz < 4 + jj) throw "FAT boundary crossed: " + j + " 4 "+ssz;
+		if(ssz < 4 + jj) throw new Error("FAT boundary crossed: " + j + " 4 "+ssz);
 		if(!sectors[addr]) break;
 		j = __readInt32LE(sectors[addr], jj);
 	}
@@ -352,7 +353,7 @@ function make_sector_list(sectors, dir_start, fat_addrs, ssz/*:number*/)/*:any*/
 			buf_chain.push(sectors[j]);
 			var addr = fat_addrs[Math.floor(j*4/ssz)];
 			jj = ((j*4) & modulus);
-			if(ssz < 4 + jj) throw "FAT boundary crossed: " + j + " 4 "+ssz;
+			if(ssz < 4 + jj) throw new Error("FAT boundary crossed: " + j + " 4 "+ssz);
 			if(!sectors[addr]) break;
 			j = __readInt32LE(sectors[addr], jj);
 		}
diff --git a/cfb.js b/cfb.js
index 7a2127f..17bb8a5 100644
--- a/cfb.js
+++ b/cfb.js
@@ -73,7 +73,7 @@ function ReadShift(size, t) {
 
 function CheckField(hexstr, fld) {
 	var m = __hexlify(this,this.l,hexstr.length>>1);
-	if(m !== hexstr) throw fld + 'Expected ' + hexstr + ' saw ' + m;
+	if(m !== hexstr) throw new Error(fld + 'Expected ' + hexstr + ' saw ' + m);
 	this.l += hexstr.length>>1;
 }
 
@@ -86,7 +86,7 @@ function prep_blob(blob, pos) {
 /* [MS-CFB] v20130118 */
 var CFB = (function _CFB(){
 var exports = {};
-exports.version = '0.11.0';
+exports.version = '0.11.1';
 function parse(file) {
 var mver = 3; // major version
 var ssz = 512; // sector size
@@ -107,7 +107,7 @@ var mv = check_get_mver(blob);
 mver = mv[0];
 switch(mver) {
 	case 3: ssz = 512; break; case 4: ssz = 4096; break;
-	default: throw "Major Version: Expected 3 or 4 saw " + mver;
+	default: throw new Error("Major Version: Expected 3 or 4 saw " + mver);
 }
 
 /* reprocess header */
@@ -119,7 +119,7 @@ check_shifts(blob, mver);
 
 // Number of Directory Sectors
 var nds = blob.read_shift(4, 'i');
-if(mver === 3 && nds !== 0) throw '# Directory Sectors: Expected 0 saw ' + nds;
+if(mver === 3 && nds !== 0) throw new Error('# Directory Sectors: Expected 0 saw ' + nds);
 
 // Number of FAT Sectors
 //var nfs = blob.read_shift(4, 'i');
@@ -205,13 +205,14 @@ function check_shifts(blob, mver) {
 	var shift = 0x09;
 
 	// Byte Order
-	blob.chk('feff', 'Byte Order: ');
+	//blob.chk('feff', 'Byte Order: '); // note: some writers put 0xffff
+	blob.l += 2;
 
 	// Sector Shift
 	switch((shift = blob.read_shift(2))) {
-		case 0x09: if(mver !== 3) throw 'MajorVersion/SectorShift Mismatch'; break;
-		case 0x0c: if(mver !== 4) throw 'MajorVersion/SectorShift Mismatch'; break;
-		default: throw 'Sector Shift: Expected 9 or 12 saw ' + shift;
+		case 0x09: if(mver != 3) throw new Error('Sector Shift: Expected 9 saw ' + shift); break;
+		case 0x0c: if(mver != 4) throw new Error('Sector Shift: Expected 12 saw ' + shift); break;
+		default: throw new Error('Sector Shift: Expected 9 or 12 saw ' + shift);
 	}
 
 	// Mini Sector Shift
@@ -293,7 +294,7 @@ function make_find_path(FullPaths, Paths, FileIndex, files, root_name) {
 function sleuth_fat(idx, cnt, sectors, ssz, fat_addrs) {
 	var q;
 	if(idx === ENDOFCHAIN) {
-		if(cnt !== 0) throw "DIFAT chain shorter than expected";
+		if(cnt !== 0) throw new Error("DIFAT chain shorter than expected");
 	} else if(idx !== -1 /*FREESECT*/) {
 		var sector = sectors[idx], m = (ssz>>>2)-1;
 		if(!sector) return;
@@ -319,7 +320,7 @@ function get_sector_list(sectors, start, fat_addrs, ssz, chkd) {
 		buf_chain.push(sectors[j]);
 		var addr = fat_addrs[Math.floor(j*4/ssz)];
 		jj = ((j*4) & modulus);
-		if(ssz < 4 + jj) throw "FAT boundary crossed: " + j + " 4 "+ssz;
+		if(ssz < 4 + jj) throw new Error("FAT boundary crossed: " + j + " 4 "+ssz);
 		if(!sectors[addr]) break;
 		j = __readInt32LE(sectors[addr], jj);
 	}
@@ -342,7 +343,7 @@ function make_sector_list(sectors, dir_start, fat_addrs, ssz) {
 			buf_chain.push(sectors[j]);
 			var addr = fat_addrs[Math.floor(j*4/ssz)];
 			jj = ((j*4) & modulus);
-			if(ssz < 4 + jj) throw "FAT boundary crossed: " + j + " 4 "+ssz;
+			if(ssz < 4 + jj) throw new Error("FAT boundary crossed: " + j + " 4 "+ssz);
 			if(!sectors[addr]) break;
 			j = __readInt32LE(sectors[addr], jj);
 		}
diff --git a/package.json b/package.json
index b65ab24..0cfafb4 100644
--- a/package.json
+++ b/package.json
@@ -1,6 +1,6 @@
 {
   "name": "cfb",
-  "version": "0.11.0",
+  "version": "0.11.1",
   "author": "sheetjs",
   "description": "Compound File Binary File Format extractor",
   "keywords": [ "cfb", "compression", "office" ],
diff --git a/xlscfb.flow.js b/xlscfb.flow.js
index 2bd8cb5..c5b75e1 100644
--- a/xlscfb.flow.js
+++ b/xlscfb.flow.js
@@ -30,7 +30,7 @@ type SectorList = {
 /* [MS-CFB] v20130118 */
 var CFB = (function _CFB(){
 var exports = {};
-exports.version = '0.11.0';
+exports.version = '0.11.1';
 function parse(file) {
 var mver = 3; // major version
 var ssz = 512; // sector size
@@ -51,7 +51,7 @@ var mv = check_get_mver(blob);
 mver = mv[0];
 switch(mver) {
 	case 3: ssz = 512; break; case 4: ssz = 4096; break;
-	default: throw "Major Version: Expected 3 or 4 saw " + mver;
+	default: throw new Error("Major Version: Expected 3 or 4 saw " + mver);
 }
 
 /* reprocess header */
@@ -63,7 +63,7 @@ check_shifts(blob, mver);
 
 // Number of Directory Sectors
 var nds = blob.read_shift(4, 'i');
-if(mver === 3 && nds !== 0) throw '# Directory Sectors: Expected 0 saw ' + nds;
+if(mver === 3 && nds !== 0) throw new Error('# Directory Sectors: Expected 0 saw ' + nds);
 
 // Number of FAT Sectors
 //var nfs = blob.read_shift(4, 'i');
@@ -149,13 +149,14 @@ function check_shifts(blob, mver) {
 	var shift = 0x09;
 
 	// Byte Order
-	blob.chk('feff', 'Byte Order: ');
+	//blob.chk('feff', 'Byte Order: '); // note: some writers put 0xffff
+	blob.l += 2;
 
 	// Sector Shift
 	switch((shift = blob.read_shift(2))) {
-		case 0x09: if(mver !== 3) throw 'MajorVersion/SectorShift Mismatch'; break;
-		case 0x0c: if(mver !== 4) throw 'MajorVersion/SectorShift Mismatch'; break;
-		default: throw 'Sector Shift: Expected 9 or 12 saw ' + shift;
+		case 0x09: if(mver != 3) throw new Error('Sector Shift: Expected 9 saw ' + shift); break;
+		case 0x0c: if(mver != 4) throw new Error('Sector Shift: Expected 12 saw ' + shift); break;
+		default: throw new Error('Sector Shift: Expected 9 or 12 saw ' + shift);
 	}
 
 	// Mini Sector Shift
@@ -237,7 +238,7 @@ function make_find_path(FullPaths, Paths, FileIndex, files, root_name) {
 function sleuth_fat(idx, cnt, sectors, ssz, fat_addrs) {
 	var q;
 	if(idx === ENDOFCHAIN) {
-		if(cnt !== 0) throw "DIFAT chain shorter than expected";
+		if(cnt !== 0) throw new Error("DIFAT chain shorter than expected");
 	} else if(idx !== -1 /*FREESECT*/) {
 		var sector = sectors[idx], m = (ssz>>>2)-1;
 		if(!sector) return;
@@ -263,7 +264,7 @@ function get_sector_list(sectors, start, fat_addrs, ssz, chkd) {
 		buf_chain.push(sectors[j]);
 		var addr = fat_addrs[Math.floor(j*4/ssz)];
 		jj = ((j*4) & modulus);
-		if(ssz < 4 + jj) throw "FAT boundary crossed: " + j + " 4 "+ssz;
+		if(ssz < 4 + jj) throw new Error("FAT boundary crossed: " + j + " 4 "+ssz);
 		if(!sectors[addr]) break;
 		j = __readInt32LE(sectors[addr], jj);
 	}
@@ -286,7 +287,7 @@ function make_sector_list(sectors, dir_start, fat_addrs, ssz/*:number*/)/*:any*/
 			buf_chain.push(sectors[j]);
 			var addr = fat_addrs[Math.floor(j*4/ssz)];
 			jj = ((j*4) & modulus);
-			if(ssz < 4 + jj) throw "FAT boundary crossed: " + j + " 4 "+ssz;
+			if(ssz < 4 + jj) throw new Error("FAT boundary crossed: " + j + " 4 "+ssz);
 			if(!sectors[addr]) break;
 			j = __readInt32LE(sectors[addr], jj);
 		}
diff --git a/xlscfb.js b/xlscfb.js
index 5d937bc..5259536 100644
--- a/xlscfb.js
+++ b/xlscfb.js
@@ -6,7 +6,7 @@ var DO_NOT_EXPORT_CFB = true;
 /* [MS-CFB] v20130118 */
 var CFB = (function _CFB(){
 var exports = {};
-exports.version = '0.11.0';
+exports.version = '0.11.1';
 function parse(file) {
 var mver = 3; // major version
 var ssz = 512; // sector size
@@ -27,7 +27,7 @@ var mv = check_get_mver(blob);
 mver = mv[0];
 switch(mver) {
 	case 3: ssz = 512; break; case 4: ssz = 4096; break;
-	default: throw "Major Version: Expected 3 or 4 saw " + mver;
+	default: throw new Error("Major Version: Expected 3 or 4 saw " + mver);
 }
 
 /* reprocess header */
@@ -39,7 +39,7 @@ check_shifts(blob, mver);
 
 // Number of Directory Sectors
 var nds = blob.read_shift(4, 'i');
-if(mver === 3 && nds !== 0) throw '# Directory Sectors: Expected 0 saw ' + nds;
+if(mver === 3 && nds !== 0) throw new Error('# Directory Sectors: Expected 0 saw ' + nds);
 
 // Number of FAT Sectors
 //var nfs = blob.read_shift(4, 'i');
@@ -125,13 +125,14 @@ function check_shifts(blob, mver) {
 	var shift = 0x09;
 
 	// Byte Order
-	blob.chk('feff', 'Byte Order: ');
+	//blob.chk('feff', 'Byte Order: '); // note: some writers put 0xffff
+	blob.l += 2;
 
 	// Sector Shift
 	switch((shift = blob.read_shift(2))) {
-		case 0x09: if(mver !== 3) throw 'MajorVersion/SectorShift Mismatch'; break;
-		case 0x0c: if(mver !== 4) throw 'MajorVersion/SectorShift Mismatch'; break;
-		default: throw 'Sector Shift: Expected 9 or 12 saw ' + shift;
+		case 0x09: if(mver != 3) throw new Error('Sector Shift: Expected 9 saw ' + shift); break;
+		case 0x0c: if(mver != 4) throw new Error('Sector Shift: Expected 12 saw ' + shift); break;
+		default: throw new Error('Sector Shift: Expected 9 or 12 saw ' + shift);
 	}
 
 	// Mini Sector Shift
@@ -213,7 +214,7 @@ function make_find_path(FullPaths, Paths, FileIndex, files, root_name) {
 function sleuth_fat(idx, cnt, sectors, ssz, fat_addrs) {
 	var q;
 	if(idx === ENDOFCHAIN) {
-		if(cnt !== 0) throw "DIFAT chain shorter than expected";
+		if(cnt !== 0) throw new Error("DIFAT chain shorter than expected");
 	} else if(idx !== -1 /*FREESECT*/) {
 		var sector = sectors[idx], m = (ssz>>>2)-1;
 		if(!sector) return;
@@ -239,7 +240,7 @@ function get_sector_list(sectors, start, fat_addrs, ssz, chkd) {
 		buf_chain.push(sectors[j]);
 		var addr = fat_addrs[Math.floor(j*4/ssz)];
 		jj = ((j*4) & modulus);
-		if(ssz < 4 + jj) throw "FAT boundary crossed: " + j + " 4 "+ssz;
+		if(ssz < 4 + jj) throw new Error("FAT boundary crossed: " + j + " 4 "+ssz);
 		if(!sectors[addr]) break;
 		j = __readInt32LE(sectors[addr], jj);
 	}
@@ -262,7 +263,7 @@ function make_sector_list(sectors, dir_start, fat_addrs, ssz) {
 			buf_chain.push(sectors[j]);
 			var addr = fat_addrs[Math.floor(j*4/ssz)];
 			jj = ((j*4) & modulus);
-			if(ssz < 4 + jj) throw "FAT boundary crossed: " + j + " 4 "+ssz;
+			if(ssz < 4 + jj) throw new Error("FAT boundary crossed: " + j + " 4 "+ssz);
 			if(!sectors[addr]) break;
 			j = __readInt32LE(sectors[addr], jj);
 		}