diff --git a/spring-batch-core/src/main/java/org/springframework/batch/core/repository/dao/MapExecutionContextDao.java b/spring-batch-core/src/main/java/org/springframework/batch/core/repository/dao/MapExecutionContextDao.java
index 80a9c0961..94c54c423 100644
--- a/spring-batch-core/src/main/java/org/springframework/batch/core/repository/dao/MapExecutionContextDao.java
+++ b/spring-batch-core/src/main/java/org/springframework/batch/core/repository/dao/MapExecutionContextDao.java
@@ -27,8 +27,9 @@ import org.springframework.batch.support.transaction.TransactionAwareProxyFactor
 /**
  * In-memory implementation of {@link ExecutionContextDao} backed by static
  * maps.
- *
+ * 
  * @author Robert Kasanicky
+ * @author Dave Syer
  */
 public class MapExecutionContextDao implements ExecutionContextDao {
 
@@ -52,7 +53,10 @@ public class MapExecutionContextDao implements ExecutionContextDao {
 	}
 
 	public void updateExecutionContext(StepExecution stepExecution) {
-		contextsByStepExecutionId.put(stepExecution.getId(), copy(stepExecution.getExecutionContext()));
+		ExecutionContext executionContext = stepExecution.getExecutionContext();
+		if (executionContext != null) {
+			contextsByStepExecutionId.put(stepExecution.getId(), copy(executionContext));
+		}
 	}
 
 	public ExecutionContext getExecutionContext(JobExecution jobExecution) {
@@ -60,7 +64,10 @@ public class MapExecutionContextDao implements ExecutionContextDao {
 	}
 
 	public void updateExecutionContext(JobExecution jobExecution) {
-		contextsByJobExecutionId.put(jobExecution.getId(), copy(jobExecution.getExecutionContext()));
+		ExecutionContext executionContext = jobExecution.getExecutionContext();
+		if (executionContext != null) {
+			contextsByJobExecutionId.put(jobExecution.getId(), copy(executionContext));
+		}
 	}
 
 	public void saveExecutionContext(JobExecution jobExecution) {
diff --git a/spring-batch-infrastructure/src/main/java/org/springframework/batch/support/transaction/TransactionAwareProxyFactory.java b/spring-batch-infrastructure/src/main/java/org/springframework/batch/support/transaction/TransactionAwareProxyFactory.java
index df069203a..b6e857afd 100644
--- a/spring-batch-infrastructure/src/main/java/org/springframework/batch/support/transaction/TransactionAwareProxyFactory.java
+++ b/spring-batch-infrastructure/src/main/java/org/springframework/batch/support/transaction/TransactionAwareProxyFactory.java
@@ -67,7 +67,7 @@ public class TransactionAwareProxyFactory<T> {
 	 * @return an independent copy
 	 */
 	@SuppressWarnings("unchecked")
-	protected final T begin(T target) {
+	protected synchronized final T begin(T target) {
 		if (target instanceof List) {
 			return (T) new ArrayList((List) target);
 		}
@@ -91,7 +91,7 @@ public class TransactionAwareProxyFactory<T> {
 	 * @param target the original target of the factory.
 	 */
 	@SuppressWarnings("unchecked")
-	protected void commit(T copy, T target) {
+	protected synchronized void commit(T copy, T target) {
 		if (target instanceof Collection) {
 			((Collection) target).clear();
 			((Collection) target).addAll((Collection) copy);