diff --git a/index.js b/index.js
index 56f7c0b..1d09e26 100644
--- a/index.js
+++ b/index.js
@@ -44,24 +44,21 @@ function rangeParser (size, str, options) {
 
   // parse all ranges
   for (var i = 0; i < arr.length; i++) {
-    var range = arr[i].split('-')
-    var start = parseInt(range[0], 10)
-    var end = parseInt(range[1], 10)
+    var indexOf = arr[i].indexOf('-')
+    if (indexOf === -1) {
+      return -2
+    }
+
+    var startStr = arr[i].slice(0, indexOf).trim()
+    var endStr = arr[i].slice(indexOf + 1).trim()
 
-    // -nnn
-    if (isNaN(start)) {
-      if (range[0].length > 0) {
-        return -2
-      }
+    var start = parsePos(startStr)
+    var end = parsePos(endStr)
 
+    if (startStr.length === 0) {
       start = size - end
       end = size - 1
-    // nnn-
-    } else if (isNaN(end)) {
-      if (range[1].length > 0) {
-        return -2
-      }
-
+    } else if (endStr.length === 0) {
       end = size - 1
     }
 
@@ -70,8 +67,12 @@ function rangeParser (size, str, options) {
       end = size - 1
     }
 
+    if (isNaN(start) || isNaN(end)) {
+      return -2
+    }
+
     // invalid or unsatisifiable
-    if (isNaN(start) || isNaN(end) || start > end || start < 0) {
+    if (start > end || start < 0) {
       continue
     }
 
@@ -92,6 +93,16 @@ function rangeParser (size, str, options) {
     : ranges
 }
 
+/**
+ * Parse string to integer.
+ * @private
+ */
+
+function parsePos (str) {
+  if (/^\d+$/.test(str)) return Number(str)
+  return NaN
+}
+
 /**
  * Combine overlapping & adjacent ranges.
  * @private
diff --git a/test/range-parser.js b/test/range-parser.js
index 0d75354..f882a93 100644
--- a/test/range-parser.js
+++ b/test/range-parser.js
@@ -21,6 +21,34 @@ describe('parseRange(len, str)', function () {
     assert.strictEqual(parse(200, 'bytes=100-x'), -2)
   })
 
+  it('should return -2 for invalid range format', function () {
+    assert.strictEqual(parse(200, 'bytes=--100'), -2)
+    assert.strictEqual(parse(200, 'bytes=100--200'), -2)
+    assert.strictEqual(parse(200, 'bytes=-'), -2)
+    assert.strictEqual(parse(200, 'bytes= - '), -2)
+  })
+
+  it('should return -2 with multiple dashes in range', function () {
+    assert.strictEqual(parse(200, 'bytes=100-200-300'), -2)
+  })
+
+  it('should return -2 for negative start byte position', function () {
+    assert.strictEqual(parse(200, 'bytes=-100-150'), -2)
+  })
+
+  it('should return -2 for invalid number format', function () {
+    assert.strictEqual(parse(200, 'bytes=01a-150'), -2)
+    assert.strictEqual(parse(200, 'bytes=100-15b0'), -2)
+  })
+
+  it('should return -1 for unsatisfiable range', function () {
+    assert.strictEqual(parse(200, 'bytes=500-600'), -1)
+  })
+
+  it('should return -1 for unsatisfiable range with multiple ranges', function () {
+    assert.strictEqual(parse(200, 'bytes=500-600,601-700'), -1)
+  })
+
   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)
@@ -99,6 +127,15 @@ describe('parseRange(len, str)', function () {
     deepEqual(range[0], { start: 0, end: 199 })
   })
 
+  it('should parse str with whitespace', function () {
+    var range = parse(1000, 'bytes=   40-80 , 81-90 , -1 ')
+    assert.strictEqual(range.type, 'bytes')
+    assert.strictEqual(range.length, 3)
+    deepEqual(range[0], { start: 40, end: 80 })
+    deepEqual(range[1], { start: 81, end: 90 })
+    deepEqual(range[2], { start: 999, end: 999 })
+  })
+
   it('should parse non-byte range', function () {
     var range = parse(1000, 'items=0-5')
     assert.strictEqual(range.type, 'items')