diff --git a/spring-batch-infrastructure/src/main/java/org/springframework/batch/item/file/transform/PrefixMatchingCompositeLineTokenizer.java b/spring-batch-infrastructure/src/main/java/org/springframework/batch/item/file/transform/PrefixMatchingCompositeLineTokenizer.java
index 21fed00b8..597542250 100644
--- a/spring-batch-infrastructure/src/main/java/org/springframework/batch/item/file/transform/PrefixMatchingCompositeLineTokenizer.java
+++ b/spring-batch-infrastructure/src/main/java/org/springframework/batch/item/file/transform/PrefixMatchingCompositeLineTokenizer.java
@@ -56,13 +56,14 @@ public class PrefixMatchingCompositeLineTokenizer implements LineTokenizer, Init
 
 		if (line != null) {
 			for (String key : delegates.keySet()) {
-				if ("".equals(key)) {
-					defaultDelegate = delegates.get(key);
-					// don't break here or the delegate may not be found
-				}
-				else if (line.startsWith(key)) {
-					delegate = delegates.get(key);
-					break;
+				if (key != null) {
+					if ("".equals(key)) {
+						defaultDelegate = delegates.get(key);
+					}
+					else if (line.startsWith(key)) {
+						delegate = delegates.get(key);
+						break;
+					}
 				}
 			}
 
diff --git a/spring-batch-infrastructure/src/test/java/org/springframework/batch/item/file/transform/PrefixMatchingCompositeLineTokenizerTests.java b/spring-batch-infrastructure/src/test/java/org/springframework/batch/item/file/transform/PrefixMatchingCompositeLineTokenizerTests.java
index bca65b7df..2536ccc61 100644
--- a/spring-batch-infrastructure/src/test/java/org/springframework/batch/item/file/transform/PrefixMatchingCompositeLineTokenizerTests.java
+++ b/spring-batch-infrastructure/src/test/java/org/springframework/batch/item/file/transform/PrefixMatchingCompositeLineTokenizerTests.java
@@ -49,16 +49,41 @@ public class PrefixMatchingCompositeLineTokenizerTests {
 	@Test
 	public void testNullLineWithKey() throws Exception {
 		Map<String, LineTokenizer> map = new HashMap<String, LineTokenizer>();
-		map.put(null, new DelimitedLineTokenizer());
+		map.put(null, new LineTokenizer() {
+			public FieldSet tokenize(String line) {
+				return new DefaultFieldSet(new String[] { "a" });
+			}
+		});
 		map.put("foo", new LineTokenizer() {
 			public FieldSet tokenize(String line) {
-				return null;
+				return new DefaultFieldSet(new String[] { "b" });
 			}
 		});
 		tokenizer.setTokenizers(map);
 		tokenizer.afterPropertiesSet();
 		FieldSet fields = tokenizer.tokenize(null);
-		assertEquals(0, fields.getFieldCount());
+		assertEquals(1, fields.getFieldCount());
+		assertEquals("a", fields.readString(0));
+	}
+
+	@Test
+	public void testNullKey() throws Exception {
+		Map<String, LineTokenizer> map = new HashMap<String, LineTokenizer>();
+		map.put(null, new LineTokenizer() {
+			public FieldSet tokenize(String line) {
+				return new DefaultFieldSet(new String[] { "a" });
+			}
+		});
+		map.put("foo", new LineTokenizer() {
+			public FieldSet tokenize(String line) {
+				return new DefaultFieldSet(new String[] { "b" });
+			}
+		});
+		tokenizer.setTokenizers(map);
+		tokenizer.afterPropertiesSet();
+		FieldSet fields = tokenizer.tokenize("foo");
+		assertEquals(1, fields.getFieldCount());
+		assertEquals("b", fields.readString(0));
 	}
 
 	@Test