diff --git a/src/java/org/apache/poi/poifs/filesystem/DocumentInputStream.java b/src/java/org/apache/poi/poifs/filesystem/DocumentInputStream.java
index 0f581aa36a..db152cef80 100644
--- a/src/java/org/apache/poi/poifs/filesystem/DocumentInputStream.java
+++ b/src/java/org/apache/poi/poifs/filesystem/DocumentInputStream.java
@@ -236,7 +236,7 @@ public class DocumentInputStream
             _tiny_buffer = new byte[ 1 ];
         }
         _document.read(_tiny_buffer, _current_offset++);
-        return _tiny_buffer[ 0 ];
+        return ((int)_tiny_buffer[ 0 ]) & 0x000000FF;
     }
 
     /**
diff --git a/src/testcases/org/apache/poi/poifs/filesystem/TestDocumentInputStream.java b/src/testcases/org/apache/poi/poifs/filesystem/TestDocumentInputStream.java
index e77fee566a..f3c15227c0 100644
--- a/src/testcases/org/apache/poi/poifs/filesystem/TestDocumentInputStream.java
+++ b/src/testcases/org/apache/poi/poifs/filesystem/TestDocumentInputStream.java
@@ -217,8 +217,10 @@ public class TestDocumentInputStream
 
         for (int j = 0; j < _workbook_size; j++)
         {
+	    int b = stream.read();
+	    assertTrue("checking sign of " + j, b >= 0);
             assertEquals("validating byte " + j, _workbook_data[ j ],
-                         ( byte ) stream.read());
+                         ( byte ) b);
             remaining--;
             assertEquals("checking remaining after reading byte " + j,
                          remaining, stream.available());