diff --git a/public/java/src/org/broadinstitute/sting/utils/nanoScheduler/NanoScheduler.java b/public/java/src/org/broadinstitute/sting/utils/nanoScheduler/NanoScheduler.java
index fcc6a5723..63ae1958c 100644
--- a/public/java/src/org/broadinstitute/sting/utils/nanoScheduler/NanoScheduler.java
+++ b/public/java/src/org/broadinstitute/sting/utils/nanoScheduler/NanoScheduler.java
@@ -85,6 +85,7 @@ public class NanoScheduler<InputType, MapType, ReduceType> {
      * The number of parallel map threads in use with this NanoScheduler
      * @return
      */
+    @Ensures("result > 0")
     public int getnThreads() {
         return nThreads;
     }
@@ -93,6 +94,7 @@ public class NanoScheduler<InputType, MapType, ReduceType> {
      * The input buffer size used by this NanoScheduler
      * @return
      */
+    @Ensures("result > 0")
     public int getBufferSize() {
         return bufferSize;
     }
@@ -101,6 +103,7 @@ public class NanoScheduler<InputType, MapType, ReduceType> {
      * The grouping size used by this NanoScheduler
      * @return
      */
+    @Ensures("result > 0")
     public int getMapGroupSize() {
         return mapGroupSize;
     }
@@ -149,8 +152,10 @@ public class NanoScheduler<InputType, MapType, ReduceType> {
                               final MapFunction<InputType, MapType> map,
                               final ReduceType initialValue,
                               final ReduceFunction<MapType, ReduceType> reduce) {
-        if ( isShutdown() )
-            throw new IllegalStateException("execute called on already shutdown NanoScheduler");
+        if ( isShutdown() ) throw new IllegalStateException("execute called on already shutdown NanoScheduler");
+        if ( inputReader == null ) throw new IllegalArgumentException("inputReader cannot be null");
+        if ( map == null ) throw new IllegalArgumentException("map function cannot be null");
+        if ( reduce == null ) throw new IllegalArgumentException("reduce function cannot be null");
 
         if ( getnThreads() == 1 ) {
             return executeSingleThreaded(inputReader, map, initialValue, reduce);
@@ -206,7 +211,7 @@ public class NanoScheduler<InputType, MapType, ReduceType> {
         return sum;
     }
 
-    @Requires("! mapQueue.isEmpty()")
+    @Requires({"reduce != null", "! mapQueue.isEmpty()"})
     private ReduceType reduceParallel(final ReduceFunction<MapType, ReduceType> reduce,
                                       final Queue<Future<List<MapType>>> mapQueue,
                                       final ReduceType initSum)
@@ -240,7 +245,7 @@ public class NanoScheduler<InputType, MapType, ReduceType> {
         return inputs;
     }
 
-    @Ensures("result.size() == inputs.size()")
+    @Requires({"map != null", "! inputs.isEmpty()"})
     private Queue<Future<List<MapType>>> submitMapJobs(final MapFunction<InputType, MapType> map,
                                                        final ExecutorService executor,
                                                        final List<InputType> inputs) {
@@ -262,11 +267,13 @@ public class NanoScheduler<InputType, MapType, ReduceType> {
         final List<InputType> inputs;
         final MapFunction<InputType, MapType> map;
 
+        @Requires({"map != null", "inputs.size() <= getMapGroupSize()"})
         private CallableMap(final MapFunction<InputType, MapType> map, final List<InputType> inputs) {
             this.inputs = inputs;
             this.map = map;
         }
 
+        @Ensures("result.size() == inputs.size()")
         @Override public List<MapType> call() throws Exception {
             final List<MapType> outputs = new LinkedList<MapType>();
             for ( final InputType input : inputs )
diff --git a/public/java/test/org/broadinstitute/sting/utils/nanoScheduler/NanoSchedulerUnitTest.java b/public/java/test/org/broadinstitute/sting/utils/nanoScheduler/NanoSchedulerUnitTest.java
index 211e43dc1..454441240 100644
--- a/public/java/test/org/broadinstitute/sting/utils/nanoScheduler/NanoSchedulerUnitTest.java
+++ b/public/java/test/org/broadinstitute/sting/utils/nanoScheduler/NanoSchedulerUnitTest.java
@@ -21,7 +21,12 @@ public class NanoSchedulerUnitTest extends BaseTest {
     }
 
     private class ReduceSum implements ReduceFunction<Integer, Integer> {
-        @Override public Integer apply(Integer one, Integer sum) { return one + sum; }
+        int prevOne = Integer.MIN_VALUE;
+
+        @Override public Integer apply(Integer one, Integer sum) {
+            Assert.assertTrue(prevOne < one, "Reduce came in out of order.  Prev " + prevOne + " cur " + one);
+            return one + sum;
+        }
     }
 
     private static int sum2x(final int start, final int end) {