OR query does not use middle field of a compound index

db.test.insert({f1: 10, f2: 10, f3: 20 }) db.test.insert({f1: 10, f2: 30, f3: 20 }) db.test.createIndex({f2: 1, f1: 1, f3: 1})   db.test.find({ f1: 10, $or: [ { f2: 10, f3: 20 }, {f2: 30, f3: 20 } ] }) The query plan will have two index scans with the following bounds: "indexBounds" : { "f2" : [ "[30.0, 30.0]" ], "f1" : [ "[MinKey, MaxKey]" ], "f3" : [ "[20.0, 20.0]" ] } Note the [MinKey, MaxKey] on the bounds for f1. This should be [10, 10] , from the condition in the query