diff --git a/headers.js b/headers.js
index eeb2842..69f4439 100644
--- a/headers.js
+++ b/headers.js
@@ -2,6 +2,16 @@ var ZEROS = '0000000000000000000';
 var ZERO_OFFSET = '0'.charCodeAt(0);
 var USTAR = 'ustar00';
 
+function clamp(index, len, defaultValue) {
+  if (typeof index !== 'number') return defaultValue;
+  index = ~~index;  // Coerce to integer.
+  if (index >= len) return len;
+  if (index >= 0) return index;
+  index += len;
+  if (index >= 0) return index;
+  return 0;
+}
+
 var toType = function(flag) {
 	switch (flag) {
 		case 0:
@@ -19,7 +29,7 @@ var toType = function(flag) {
 		case 6:
 		return 'fifo';
 		case 7:
-		return 'contiguous-file'
+		return 'contiguous-file';
 		case 72:
 		return 'pax-header';
 	}
@@ -78,7 +88,7 @@ var encodeOct = function(val, n) {
 };
 
 var decodeOct = function(val, offset) {
-	return parseInt(val.slice(offset, indexOf(val, 32, offset)).toString(), 8);
+	return parseInt(val.slice(offset, clamp(indexOf(val, 32, offset), val.length, val.length)).toString(), 8);
 };
 
 var decodeStr = function(val, offset) {
diff --git a/test/extract.js b/test/extract.js
index 5f9f6db..f40d060 100644
--- a/test/extract.js
+++ b/test/extract.js
@@ -4,6 +4,16 @@ var fixtures = require('./fixtures');
 var concat = require('concat-stream');
 var fs = require('fs');
 
+function clamp(index, len, defaultValue) {
+  if (typeof index !== 'number') return defaultValue;
+  index = ~~index;  // Coerce to integer.
+  if (index >= len) return len;
+  if (index >= 0) return index;
+  index += len;
+  if (index >= 0) return index;
+  return 0;
+}
+
 test('one-file', function(t) {
 	t.plan(3);
 
@@ -76,7 +86,7 @@ test('chunked-one-file', function(t) {
 	var b = fs.readFileSync(fixtures.ONE_FILE_TAR);
 
 	for (var i = 0; i < b.length; i += 321) {
-		extract.write(b.slice(i, i+321));
+		extract.write(b.slice(i, clamp(i+321, b.length, b.length)));
 	}
 	extract.end();
 });
@@ -203,7 +213,7 @@ test('chunked-multi-file', function(t) {
 
 	var b = fs.readFileSync(fixtures.MULTI_FILE_TAR);
 	for (var i = 0; i < b.length; i += 321) {
-		extract.write(b.slice(i, i+321));
+		extract.write(b.slice(i, clamp(i+321, b.length, b.length)));
 	}
 	extract.end();
 });