diff --git a/src/mongo/db/commands/mr.cpp b/src/mongo/db/commands/mr.cpp
index 6d2fb37..f65ac56 100644
--- a/src/mongo/db/commands/mr.cpp
+++ b/src/mongo/db/commands/mr.cpp
@@ -1194,7 +1194,17 @@ namespace mongo {
 
                         Timer mt;
                         // go through each doc
+                        long long int iter = 0;
                         while ( cursor->ok() ) {
+                            if (++iter % 1000 == 0) {
+                                // try to yield lock regularly
+                                ClientCursor::YieldLock yield (cursor.get());
+                                if ( ! yield.stillOk() ) {
+                                    break;
+                                }
+                                killCurrentOp.checkForInterrupt();
+                            }
+
                             if ( ! cursor->currentMatches() ) {
                                 cursor->advance();
                                 continue;