Note: I did this with mlaunch v 1.1.7 First, download the attached tarball and go to the directory you saved it to. $ tar xvf mlaunch_data_failed_sparse_hint.tar.gz $ mlaunch start $ mongo mongos> db.foo.explain( "executionStats" ).find( { a : 12, b : 25, c : 8 } ).hint( { e : 1 } ) Expected result: The query is executed, but misses a document that lacks an "e" field (and therefore an index entry on { e : 1 } Actual result: An error is thrown: 2015-01-27T10:35:27.605-0500 E QUERY Error: explain failed: { "ok" : 0, "errmsg" : "Explain command on shard cross-mb-air.local:27018 failed, caused by: { ok: 0.0, errmsg: \" error processing query: ns=test.foo limit=0 skip=0\nTree: $and\n a == 12.0\n b == 25.0\n c == 8.0\nSort: {}\nProj: {}\n planner returned error: bad hint\ ", code: 2, $gleStats: { lastOpTime: Timestamp 0|0, electionId: ObjectId( '54c7aef96a0ab41446ee1188' ) } }" , "code" : 2 } at Error (<anonymous>) at Function.throwOrReturn (src/mongo/shell/explainable.js:34:19) at constructor.finish (src/mongo/shell/explain_query.js:188:36) at constructor.shellPrint (src/mongo/shell/explain_query.js:228:31) at shellPrintHelper (src/mongo/shell/utils.js:396:18) at (shell2):1:19 at src/mongo/shell/explainable.js:34