diff --git a/Sources/MODCursor.m b/Sources/MODCursor.m
index a5f6bc45..f9d056cd 100644
--- a/Sources/MODCursor.m
+++ b/Sources/MODCursor.m
@@ -113,7 +113,7 @@ - (MODSortedMutableDictionary *)nextDocumentWithBsonData:(NSData **)bsonData err
             
             result = [[_mongoCollection.mongoServer class] objectFromBson:&(mongoCursor->current)];
             if (bsonData) {
-                *bsonData = [[[NSData alloc] initWithBytes:mongoCursor->current.data length:mongoCursor->current.dataSize] autorelease];
+                *bsonData = [[[NSData alloc] initWithBytes:mongoCursor->current.data length:bson_size(&mongoCursor->current)] autorelease];
             }
         } else if (((mongo_cursor *)_cursor)->err != MONGO_CURSOR_EXHAUSTED) {
             NSString *details = nil;
diff --git a/Sources/MODServer.h b/Sources/MODServer.h
index e468612c..f325c1c4 100644
--- a/Sources/MODServer.h
+++ b/Sources/MODServer.h
@@ -55,6 +55,7 @@ typedef struct mongo                    *mongo_ptr;
 + (NSString *)escapeQuotesForString:(NSString *)string;
 + (NSString *)escapeSlashesForString:(NSString *)string;
 + (NSString *)convertObjectToJson:(MODSortedMutableDictionary *)object pretty:(BOOL)pretty strictJson:(BOOL)strictJson;
++ (void)compareJson:(NSString *)json bsonData:(NSData *)document;
 + (void)compareJson:(NSString *)json document:(id)document;
 + (NSArray *)findAllDifferencesInObject1:(id)object1 object2:(id)object2;
 @end
\ No newline at end of file
diff --git a/Sources/MODServer_utils.m b/Sources/MODServer_utils.m
index 38579e8b..930cddf3 100644
--- a/Sources/MODServer_utils.m
+++ b/Sources/MODServer_utils.m
@@ -618,6 +618,26 @@ + (NSString *)escapeSlashesForString:(NSString *)string
     return [result autorelease];
 }
 
++ (void)compareJson:(NSString *)json bsonData:(NSData *)document
+{
+    bson bsonDocumentFromJson;
+    NSError *error;
+    
+    bson_init(&bsonDocumentFromJson);
+    [MODJsonToBsonParser bsonFromJson:&bsonDocumentFromJson json:json error:&error];
+    bson_finish(&bsonDocumentFromJson);
+    NSAssert(error == nil, @"error with document %@", document);
+    if ([document length] != bson_size(&bsonDocumentFromJson) || memcmp([document bytes], bsonDocumentFromJson.data, [document length]) != 0) {
+        NSLog(@"%@", [NSData dataWithBytes:bsonDocumentFromJson.data length:bson_size(&bsonDocumentFromJson)]);
+        NSLog(@"error with this document %@", document);
+        NSLog(@"json %@", [MODServer convertObjectToJson:[MODServer objectFromBson:&bsonDocumentFromJson] pretty:YES strictJson:NO]);
+        NSAssert([document length] == bson_size(&bsonDocumentFromJson), @"not the same size with %@", document);
+        NSAssert(memcmp([document bytes], bsonDocumentFromJson.data, [document length]) == 0, @"not the same content %@", document);
+    }
+    
+    bson_destroy(&bsonDocumentFromJson);
+}
+
 + (void)compareJson:(NSString *)json document:(id)document
 {
     bson bsonDocument;