diff --git a/python/pyspark/rdd.py b/python/pyspark/rdd.py
index 6d549b40e5698..f3b432ff248a9 100644
--- a/python/pyspark/rdd.py
+++ b/python/pyspark/rdd.py
@@ -268,6 +268,7 @@ def sample(self, withReplacement, fraction, seed):
         >>> sc.parallelize(range(0, 100)).sample(False, 0.1, 2).collect() #doctest: +SKIP
         [2, 3, 20, 21, 24, 41, 42, 66, 67, 89, 90, 98]
         """
+        assert fraction >= 0.0, "Invalid fraction value: %s" % fraction
         return self.mapPartitionsWithIndex(RDDSampler(withReplacement, fraction, seed).func, True)
 
     # this is ported from scala/spark/RDD.scala
@@ -288,6 +289,9 @@ def takeSample(self, withReplacement, num, seed):
         if (num < 0):
             raise ValueError
 
+        if (initialCount == 0):
+            return list()
+
         if initialCount > sys.maxint - 1:
             maxSelected = sys.maxint - 1
         else: