diff --git a/bits/05_buf.js b/bits/05_buf.js
index 217e5ac..378e99b 100644
--- a/bits/05_buf.js
+++ b/bits/05_buf.js
@@ -7,7 +7,7 @@ if(typeof Buffer !== 'undefined') {
 	if(!nbfs) try { Buffer.from("foo", "utf8"); } catch(e) { nbfs = true; }
 	Buffer_from = /*::((*/nbfs ? function(buf, enc) { return (enc) ? new Buffer(buf, enc) : new Buffer(buf); } : Buffer.from.bind(Buffer)/*::) :any)*/;
 	// $FlowIgnore
-	if(!Buffer.alloc) Buffer.alloc = function(n) { return new Buffer(n); };
+	if(!Buffer.alloc) Buffer.alloc = function(n) { var b = new Buffer(n); b.fill(0); return b; };
 	// $FlowIgnore
 	if(!Buffer.allocUnsafe) Buffer.allocUnsafe = function(n) { return new Buffer(n); };
 }
diff --git a/bits/67_stream.js b/bits/67_stream.js
index cdb26ce..932a29b 100644
--- a/bits/67_stream.js
+++ b/bits/67_stream.js
@@ -3,7 +3,13 @@
 		/*:: if(!file.content) throw new Error("unreachable"); */
 		if(file.size >= 0x1000) {
 			o.l = (file.start+1) << 9;
-			for(j = 0; j < file.size; ++j) o.write_shift(1, file.content[j]);
-			for(; j & 0x1FF; ++j) o.write_shift(1, 0);
+			if (has_buf && Buffer.isBuffer(file.content)) {
+				file.content.copy(o, o.l, 0, file.size);
+				// o is a 0-filled Buffer so just set next offset
+				o.l += (file.size + 511) & -512;
+			} else {
+				for(j = 0; j < file.size; ++j) o.write_shift(1, file.content[j]);
+				for(; j & 0x1FF; ++j) o.write_shift(1, 0);
+			}
 		}
 	}
diff --git a/bits/68_mini.js b/bits/68_mini.js
index 9b080b2..fad30a9 100644
--- a/bits/68_mini.js
+++ b/bits/68_mini.js
@@ -2,8 +2,19 @@
 		file = cfb.FileIndex[i];
 		/*:: if(!file.content) throw new Error("unreachable"); */
 		if(file.size > 0 && file.size < 0x1000) {
-			for(j = 0; j < file.size; ++j) o.write_shift(1, file.content[j]);
-			for(; j & 0x3F; ++j) o.write_shift(1, 0);
+			if (has_buf && Buffer.isBuffer(file.content)) {
+				file.content.copy(o, o.l, 0, file.size);
+				// o is a 0-filled Buffer so just set next offset
+				o.l += (file.size + 63) & -64;
+			} else {
+				for(j = 0; j < file.size; ++j) o.write_shift(1, file.content[j]);
+				for(; j & 0x3F; ++j) o.write_shift(1, 0);
+			}
 		}
 	}
-	while(o.l < o.length) o.write_shift(1, 0);
+	if (has_buf) {
+		o.l = o.length;
+	} else {
+		// When using Buffer, already 0-filled
+		while(o.l < o.length) o.write_shift(1, 0);
+	}
diff --git a/cfb.flow.js b/cfb.flow.js
index d884851..3cc8e23 100644
--- a/cfb.flow.js
+++ b/cfb.flow.js
@@ -57,7 +57,7 @@ if(typeof Buffer !== 'undefined') {
 	if(!nbfs) try { Buffer.from("foo", "utf8"); } catch(e) { nbfs = true; }
 	Buffer_from = /*::((*/nbfs ? function(buf, enc) { return (enc) ? new Buffer(buf, enc) : new Buffer(buf); } : Buffer.from.bind(Buffer)/*::) :any)*/;
 	// $FlowIgnore
-	if(!Buffer.alloc) Buffer.alloc = function(n) { return new Buffer(n); };
+	if(!Buffer.alloc) Buffer.alloc = function(n) { var b = new Buffer(n); b.fill(0); return b; };
 	// $FlowIgnore
 	if(!Buffer.allocUnsafe) Buffer.allocUnsafe = function(n) { return new Buffer(n); };
 }
@@ -936,19 +936,36 @@ function _write(cfb/*:CFBContainer*/, options/*:CFBWriteOpts*/)/*:RawBytes|strin
 		/*:: if(!file.content) throw new Error("unreachable"); */
 		if(file.size >= 0x1000) {
 			o.l = (file.start+1) << 9;
-			for(j = 0; j < file.size; ++j) o.write_shift(1, file.content[j]);
-			for(; j & 0x1FF; ++j) o.write_shift(1, 0);
+			if (has_buf && Buffer.isBuffer(file.content)) {
+				file.content.copy(o, o.l, 0, file.size);
+				// o is a 0-filled Buffer so just set next offset
+				o.l += (file.size + 511) & -512;
+			} else {
+				for(j = 0; j < file.size; ++j) o.write_shift(1, file.content[j]);
+				for(; j & 0x1FF; ++j) o.write_shift(1, 0);
+			}
 		}
 	}
 	for(i = 1; i < cfb.FileIndex.length; ++i) {
 		file = cfb.FileIndex[i];
 		/*:: if(!file.content) throw new Error("unreachable"); */
 		if(file.size > 0 && file.size < 0x1000) {
-			for(j = 0; j < file.size; ++j) o.write_shift(1, file.content[j]);
-			for(; j & 0x3F; ++j) o.write_shift(1, 0);
+			if (has_buf && Buffer.isBuffer(file.content)) {
+				file.content.copy(o, o.l, 0, file.size);
+				// o is a 0-filled Buffer so just set next offset
+				o.l += (file.size + 63) & -64;
+			} else {
+				for(j = 0; j < file.size; ++j) o.write_shift(1, file.content[j]);
+				for(; j & 0x3F; ++j) o.write_shift(1, 0);
+			}
 		}
 	}
-	while(o.l < o.length) o.write_shift(1, 0);
+	if (has_buf) {
+		o.l = o.length;
+	} else {
+		// When using Buffer, already 0-filled
+		while(o.l < o.length) o.write_shift(1, 0);
+	}
 	return o;
 }
 /* [MS-CFB] 2.6.4 (Unicode 3.0.1 case conversion) */
diff --git a/cfb.js b/cfb.js
index a3b5550..c4267b2 100644
--- a/cfb.js
+++ b/cfb.js
@@ -57,7 +57,7 @@ if(typeof Buffer !== 'undefined') {
 	if(!nbfs) try { Buffer.from("foo", "utf8"); } catch(e) { nbfs = true; }
 	Buffer_from = nbfs ? function(buf, enc) { return (enc) ? new Buffer(buf, enc) : new Buffer(buf); } : Buffer.from.bind(Buffer);
 	// $FlowIgnore
-	if(!Buffer.alloc) Buffer.alloc = function(n) { return new Buffer(n); };
+	if(!Buffer.alloc) Buffer.alloc = function(n) { var b = new Buffer(n); b.fill(0); return b; };
 	// $FlowIgnore
 	if(!Buffer.allocUnsafe) Buffer.allocUnsafe = function(n) { return new Buffer(n); };
 }
@@ -914,18 +914,35 @@ flen = file.content.length;
 		file = cfb.FileIndex[i];
 if(file.size >= 0x1000) {
 			o.l = (file.start+1) << 9;
-			for(j = 0; j < file.size; ++j) o.write_shift(1, file.content[j]);
-			for(; j & 0x1FF; ++j) o.write_shift(1, 0);
+			if (has_buf && Buffer.isBuffer(file.content)) {
+				file.content.copy(o, o.l, 0, file.size);
+				// o is a 0-filled Buffer so just set next offset
+				o.l += (file.size + 511) & -512;
+			} else {
+				for(j = 0; j < file.size; ++j) o.write_shift(1, file.content[j]);
+				for(; j & 0x1FF; ++j) o.write_shift(1, 0);
+			}
 		}
 	}
 	for(i = 1; i < cfb.FileIndex.length; ++i) {
 		file = cfb.FileIndex[i];
 if(file.size > 0 && file.size < 0x1000) {
-			for(j = 0; j < file.size; ++j) o.write_shift(1, file.content[j]);
-			for(; j & 0x3F; ++j) o.write_shift(1, 0);
+			if (has_buf && Buffer.isBuffer(file.content)) {
+				file.content.copy(o, o.l, 0, file.size);
+				// o is a 0-filled Buffer so just set next offset
+				o.l += (file.size + 63) & -64;
+			} else {
+				for(j = 0; j < file.size; ++j) o.write_shift(1, file.content[j]);
+				for(; j & 0x3F; ++j) o.write_shift(1, 0);
+			}
 		}
 	}
-	while(o.l < o.length) o.write_shift(1, 0);
+	if (has_buf) {
+		o.l = o.length;
+	} else {
+		// When using Buffer, already 0-filled
+		while(o.l < o.length) o.write_shift(1, 0);
+	}
 	return o;
 }
 /* [MS-CFB] 2.6.4 (Unicode 3.0.1 case conversion) */
diff --git a/xlscfb.flow.js b/xlscfb.flow.js
index 9991d94..1eb3a01 100644
--- a/xlscfb.flow.js
+++ b/xlscfb.flow.js
@@ -784,19 +784,36 @@ function _write(cfb/*:CFBContainer*/, options/*:CFBWriteOpts*/)/*:RawBytes|strin
 		/*:: if(!file.content) throw new Error("unreachable"); */
 		if(file.size >= 0x1000) {
 			o.l = (file.start+1) << 9;
-			for(j = 0; j < file.size; ++j) o.write_shift(1, file.content[j]);
-			for(; j & 0x1FF; ++j) o.write_shift(1, 0);
+			if (has_buf && Buffer.isBuffer(file.content)) {
+				file.content.copy(o, o.l, 0, file.size);
+				// o is a 0-filled Buffer so just set next offset
+				o.l += (file.size + 511) & -512;
+			} else {
+				for(j = 0; j < file.size; ++j) o.write_shift(1, file.content[j]);
+				for(; j & 0x1FF; ++j) o.write_shift(1, 0);
+			}
 		}
 	}
 	for(i = 1; i < cfb.FileIndex.length; ++i) {
 		file = cfb.FileIndex[i];
 		/*:: if(!file.content) throw new Error("unreachable"); */
 		if(file.size > 0 && file.size < 0x1000) {
-			for(j = 0; j < file.size; ++j) o.write_shift(1, file.content[j]);
-			for(; j & 0x3F; ++j) o.write_shift(1, 0);
+			if (has_buf && Buffer.isBuffer(file.content)) {
+				file.content.copy(o, o.l, 0, file.size);
+				// o is a 0-filled Buffer so just set next offset
+				o.l += (file.size + 63) & -64;
+			} else {
+				for(j = 0; j < file.size; ++j) o.write_shift(1, file.content[j]);
+				for(; j & 0x3F; ++j) o.write_shift(1, 0);
+			}
 		}
 	}
-	while(o.l < o.length) o.write_shift(1, 0);
+	if (has_buf) {
+		o.l = o.length;
+	} else {
+		// When using Buffer, already 0-filled
+		while(o.l < o.length) o.write_shift(1, 0);
+	}
 	return o;
 }
 /* [MS-CFB] 2.6.4 (Unicode 3.0.1 case conversion) */
diff --git a/xlscfb.js b/xlscfb.js
index ba81cd4..6ec3b27 100644
--- a/xlscfb.js
+++ b/xlscfb.js
@@ -746,18 +746,35 @@ flen = file.content.length;
 		file = cfb.FileIndex[i];
 if(file.size >= 0x1000) {
 			o.l = (file.start+1) << 9;
-			for(j = 0; j < file.size; ++j) o.write_shift(1, file.content[j]);
-			for(; j & 0x1FF; ++j) o.write_shift(1, 0);
+			if (has_buf && Buffer.isBuffer(file.content)) {
+				file.content.copy(o, o.l, 0, file.size);
+				// o is a 0-filled Buffer so just set next offset
+				o.l += (file.size + 511) & -512;
+			} else {
+				for(j = 0; j < file.size; ++j) o.write_shift(1, file.content[j]);
+				for(; j & 0x1FF; ++j) o.write_shift(1, 0);
+			}
 		}
 	}
 	for(i = 1; i < cfb.FileIndex.length; ++i) {
 		file = cfb.FileIndex[i];
 if(file.size > 0 && file.size < 0x1000) {
-			for(j = 0; j < file.size; ++j) o.write_shift(1, file.content[j]);
-			for(; j & 0x3F; ++j) o.write_shift(1, 0);
+			if (has_buf && Buffer.isBuffer(file.content)) {
+				file.content.copy(o, o.l, 0, file.size);
+				// o is a 0-filled Buffer so just set next offset
+				o.l += (file.size + 63) & -64;
+			} else {
+				for(j = 0; j < file.size; ++j) o.write_shift(1, file.content[j]);
+				for(; j & 0x3F; ++j) o.write_shift(1, 0);
+			}
 		}
 	}
-	while(o.l < o.length) o.write_shift(1, 0);
+	if (has_buf) {
+		o.l = o.length;
+	} else {
+		// When using Buffer, already 0-filled
+		while(o.l < o.length) o.write_shift(1, 0);
+	}
 	return o;
 }
 /* [MS-CFB] 2.6.4 (Unicode 3.0.1 case conversion) */