diff --git a/index.js b/index.js
index b7dc5c0..56f7c0b 100644
--- a/index.js
+++ b/index.js
@@ -50,10 +50,18 @@ function rangeParser (size, str, options) {
 
     // -nnn
     if (isNaN(start)) {
+      if (range[0].length > 0) {
+        return -2
+      }
+
       start = size - end
       end = size - 1
     // nnn-
     } else if (isNaN(end)) {
+      if (range[1].length > 0) {
+        return -2
+      }
+
       end = size - 1
     }
 
diff --git a/test/range-parser.js b/test/range-parser.js
index e2af8b4..0d75354 100644
--- a/test/range-parser.js
+++ b/test/range-parser.js
@@ -13,6 +13,14 @@ describe('parseRange(len, str)', function () {
     assert.strictEqual(parse(200, 'malformed'), -2)
   })
 
+  it('should return -2 for invalid start byte position', function () {
+    assert.strictEqual(parse(200, 'bytes=x-100'), -2)
+  })
+
+  it('should return -2 for invalid end byte position', function () {
+    assert.strictEqual(parse(200, 'bytes=100-x'), -2)
+  })
+
   it('should return -1 if all specified ranges are invalid', function () {
     assert.strictEqual(parse(200, 'bytes=500-20'), -1)
     assert.strictEqual(parse(200, 'bytes=500-999'), -1)