diff --git a/db/mr.cpp b/db/mr.cpp
index d0a7cb74ed4..066ade2516d 100644
--- a/db/mr.cpp
+++ b/db/mr.cpp
@@ -48,9 +48,9 @@ namespace mongo {
             for ( list<BSONObj>::iterator i=values.begin(); i!=values.end(); i++){
                 BSONObj o = *i;
                 if ( n == 0 ){
-                    reduceArgs.append( o["key"] );
+                    reduceArgs.append( o["_id"] );
                     BSONObjBuilder temp;
-                    temp.append( o["key"] );
+                    temp.append( o["_id"] );
                     key = temp.obj();
                 }
                 valueBuilder.appendAs( o["value"] , BSONObjBuilder::numStr( n++ ).c_str() );
@@ -65,7 +65,7 @@ namespace mongo {
                 return BSONObj();
             }
             BSONObjBuilder b;
-            b.append( key["key"] );
+            b.append( key["_id"] );
             s->append( b , "value" , "return" );
             return b.obj();
         }
@@ -180,7 +180,7 @@ namespace mongo {
             {
                 assert( i.more() );
                 BSONObjBuilder b;
-                b.appendAs( i.next() , "key" );
+                b.appendAs( i.next() , "_id" );
                 key = b.obj();
             }
 
@@ -224,7 +224,7 @@ namespace mongo {
                 if ( values.size() == 0 )
                     return;
                 
-                BSONObj key = values.begin()->extractFields( BSON( "key" << 1 ) );
+                BSONObj key = values.begin()->extractFields( BSON( "_id" << 1 ) );
                 
                 if ( values.size() == 1 ){
                     assert( db.count( resultColl , key  ) == 1 );
@@ -259,7 +259,6 @@ namespace mongo {
                 string finalOutputShort = finalOutput.substr( database->name.size() + 1 );
                 log(1) << "\t resultColl: " << resultColl << " short: " << resultCollShort << endl;
                 db.dropCollection( resultColl );
-                db.ensureIndex( resultColl , BSON( "key" << 1 ) );
             
                 int num = 0;
             
@@ -305,9 +304,9 @@ namespace mongo {
 
                     BSONObj prev;
                     list<BSONObj> all;
-                    BSONObj sortKey = BSON( "key" << 1 );
+                    BSONObj sortKey = BSON( "_id" << 1 );
                 
-                    cursor = db.query( resultColl, Query().sort( BSON( "key" << 1 ) ) );
+                    cursor = db.query( resultColl, Query().sort( sortKey ) );
                     while ( cursor->more() ){
                         BSONObj o = cursor->next().getOwned();
 
diff --git a/jstests/mr1.js b/jstests/mr1.js
index f50819803d5..82574ea06d4 100644
--- a/jstests/mr1.js
+++ b/jstests/mr1.js
@@ -32,7 +32,7 @@ x = db[res.result];
 assert.eq( 3 , x.find().count() , "B" );
 x.find().forEach( printjson );
 z = {};
-x.find().forEach( function(a){ z[a.key] = a.value.count; } );
+x.find().forEach( function(a){ z[a._id] = a.value.count; } );
 printjson( z );
 assert.eq( 3 , z.keySet().length , "C" );
 assert.eq( 2 , z.a , "D" );
@@ -44,7 +44,7 @@ res = db.runCommand( { mapreduce : "mr1" , map : m , reduce : r , query : { x :
 assert.eq( 2 , res.numObjects , "B" );
 x = db[res.result];
 z = {};
-x.find().forEach( function(a){ z[a.key] = a.value.count; } );
+x.find().forEach( function(a){ z[a._id] = a.value.count; } );
 assert.eq( 1 , z.a , "C1" );
 assert.eq( 1 , z.b , "C2" );
 assert.eq( 2 , z.c , "C3" );
@@ -55,7 +55,7 @@ assert.eq( 2 , res.numObjects , "B2" );
 assert.eq( "foo" , res.result , "B2-c" );
 x = db[res.result];
 z = {};
-x.find().forEach( function(a){ z[a.key] = a.value.count; } );
+x.find().forEach( function(a){ z[a._id] = a.value.count; } );
 assert.eq( 1 , z.a , "C1a" );
 assert.eq( 1 , z.b , "C2a" );
 assert.eq( 2 , z.c , "C3a" );
@@ -73,11 +73,11 @@ assert.eq( 999 , res.numObjects , "Z1" );
 x = db[res.result];
 x.find().forEach( printjson )
 assert.eq( 4 , x.find().count() , "Z2" );
-assert.eq( "a,b,c,d" , x.distinct( "key" ) , "Z3" );
-assert.eq( 2 , x.findOne( { key : "a" } ).value.count , "ZA" );
-assert.eq( 998 , x.findOne( { key : "b" } ).value.count , "ZB" );
-assert.eq( 3 , x.findOne( { key : "c" } ).value.count , "ZC" );
-assert.eq( 995 , x.findOne( { key : "d" } ).value.count , "ZD" );
+assert.eq( "a,b,c,d" , x.distinct( "_id" ) , "Z3" );
+assert.eq( 2 , x.findOne( { _id : "a" } ).value.count , "ZA" );
+assert.eq( 998 , x.findOne( { _id : "b" } ).value.count , "ZB" );
+assert.eq( 3 , x.findOne( { _id : "c" } ).value.count , "ZC" );
+assert.eq( 995 , x.findOne( { _id : "d" } ).value.count , "ZD" );
 
 print( Date.timeFunc( 
     function(){