diff --git a/HISTORY.rst b/HISTORY.rst
index 9c12ce95b..b5775bfd4 100644
--- a/HISTORY.rst
+++ b/HISTORY.rst
@@ -8,6 +8,8 @@ Bug tracker at https://github.com/giampaolo/psutil/issues
 
 - #798: [Windows] Process.open_files() returns and empty list on Windows 10.
 - #880: [Windows] Handle race condition inside psutil_net_connections.
+- #885: ValueError is raised if a negative integer is passed to cpu_percent()
+  functions.
 
 
 4.3.1 - 2016-09-01
diff --git a/psutil/__init__.py b/psutil/__init__.py
index 7a557d075..0a6f3ec6f 100644
--- a/psutil/__init__.py
+++ b/psutil/__init__.py
@@ -921,13 +921,17 @@ def cpu_percent(self, interval=None):
           >>>
         """
         blocking = interval is not None and interval > 0.0
+        if interval is not None and interval < 0:
+            raise ValueError("interval is not positive (got %r)" % interval)
         num_cpus = cpu_count() or 1
+
         if POSIX:
             def timer():
                 return _timer() * num_cpus
         else:
             def timer():
                 return sum(cpu_times())
+
         if blocking:
             st1 = timer()
             pt1 = self._proc.cpu_times()
@@ -1566,6 +1570,8 @@ def cpu_percent(interval=None, percpu=False):
     global _last_cpu_times
     global _last_per_cpu_times
     blocking = interval is not None and interval > 0.0
+    if interval is not None and interval < 0:
+        raise ValueError("interval is not positive (got %r)" % interval)
 
     def calculate(t1, t2):
         t1_all = sum(t1)
@@ -1639,6 +1645,8 @@ def cpu_times_percent(interval=None, percpu=False):
     global _last_cpu_times_2
     global _last_per_cpu_times_2
     blocking = interval is not None and interval > 0.0
+    if interval is not None and interval < 0:
+        raise ValueError("interval is not positive (got %r)" % interval)
 
     def calculate(t1, t2):
         nums = []
diff --git a/psutil/tests/test_process.py b/psutil/tests/test_process.py
index 0d7d06be3..78f057df9 100644
--- a/psutil/tests/test_process.py
+++ b/psutil/tests/test_process.py
@@ -255,6 +255,8 @@ def test_cpu_percent(self):
                 self.assertLessEqual(percent, 100.0)
             else:
                 self.assertGreaterEqual(percent, 0.0)
+        with self.assertRaises(ValueError):
+            p.cpu_percent(interval=-1)
 
     def test_cpu_times(self):
         times = psutil.Process().cpu_times()
diff --git a/psutil/tests/test_system.py b/psutil/tests/test_system.py
index f5c9abd65..4a48a52bb 100644
--- a/psutil/tests/test_system.py
+++ b/psutil/tests/test_system.py
@@ -359,6 +359,8 @@ def test_cpu_percent(self):
             new = psutil.cpu_percent(interval=None)
             self._test_cpu_percent(new, last, new)
             last = new
+        with self.assertRaises(ValueError):
+            psutil.cpu_percent(interval=-1)
 
     def test_per_cpu_percent(self):
         last = psutil.cpu_percent(interval=0.001, percpu=True)
@@ -368,6 +370,8 @@ def test_per_cpu_percent(self):
             for percent in new:
                 self._test_cpu_percent(percent, last, new)
             last = new
+        with self.assertRaises(ValueError):
+            psutil.cpu_percent(interval=-1, percpu=True)
 
     def test_cpu_times_percent(self):
         last = psutil.cpu_times_percent(interval=0.001)