diff --git a/.gitignore b/.gitignore
index daa30a3..cec3e54 100644
--- a/.gitignore
+++ b/.gitignore
@@ -1 +1,2 @@
 README.html
+/.idea
diff --git a/lib/strtok.js b/lib/strtok.js
index 4884b6f..861febe 100644
--- a/lib/strtok.js
+++ b/lib/strtok.js
@@ -231,6 +231,8 @@ exports.INT32_BE = INT32_BE;
 // the 'len' and other properties directly.
 
 var BufferType = function(l) {
+    assert.ok(l && l > 0);
+
     var self = this;
 
     self.len = l;
diff --git a/package.json b/package.json
index 3788b34..9c27d81 100644
--- a/package.json
+++ b/package.json
@@ -1,6 +1,6 @@
 {
     "name" : "strtok",
-    "version" : "0.1.0",
+    "version" : "0.1.1",
     "description" : "A streaming tokenizer",
     "author" : "Peter Griess <pg@std.in>",
     "engines" : {
diff --git a/test/test-buf.js b/test/test-buf.js
index 5a53ff8..797799f 100644
--- a/test/test-buf.js
+++ b/test/test-buf.js
@@ -19,3 +19,6 @@ util.runParseTests('\x05peter', [
         return strtok.DONE;
     }
 ]);
+
+assert.throws(function() { new strtok.BufferType(NaN); }, Error);
+assert.throws(function() { new strtok.BufferType(-1); }, Error);