diff -up mgo-9856a29383ce1c59f308dd1cf0363a79b5bef6b5/gridfs.go.fix_debugf mgo-9856a29383ce1c59f308dd1cf0363a79b5bef6b5/gridfs.go
--- mgo-9856a29383ce1c59f308dd1cf0363a79b5bef6b5/gridfs.go.fix_debugf	2018-07-05 13:36:04.000000000 +0200
+++ mgo-9856a29383ce1c59f308dd1cf0363a79b5bef6b5/gridfs.go	2019-06-03 18:29:22.680831420 +0200
@@ -657,7 +657,7 @@ func (file *GridFile) insertChunk(data [
 // an error, if any.
 func (file *GridFile) Seek(offset int64, whence int) (pos int64, err error) {
 	file.m.Lock()
-	debugf("GridFile %p: seeking for %s (whence=%d)", file, offset, whence)
+	debugf("GridFile %p: seeking for %d (whence=%d)", file, offset, whence)
 	defer file.m.Unlock()
 	switch whence {
 	case os.SEEK_SET:
diff -up mgo-9856a29383ce1c59f308dd1cf0363a79b5bef6b5/session.go.fix_debugf mgo-9856a29383ce1c59f308dd1cf0363a79b5bef6b5/session.go
--- mgo-9856a29383ce1c59f308dd1cf0363a79b5bef6b5/session.go.fix_debugf	2018-07-05 13:36:04.000000000 +0200
+++ mgo-9856a29383ce1c59f308dd1cf0363a79b5bef6b5/session.go	2019-06-03 18:29:22.682831417 +0200
@@ -3268,7 +3268,7 @@ func (db *Database) run(socket *mongoSoc
 	if result != nil {
 		err = bson.Unmarshal(data, result)
 		if err != nil {
-			debugf("Run command unmarshaling failed: %#v", op, err)
+			debugf("Run command unmarshaling failed: %#v, error: %#v", op, err)
 			return err
 		}
 		if globalDebug && globalLogger != nil {
diff -up mgo-9856a29383ce1c59f308dd1cf0363a79b5bef6b5/txn/flusher.go.fix_debugf mgo-9856a29383ce1c59f308dd1cf0363a79b5bef6b5/txn/flusher.go
--- mgo-9856a29383ce1c59f308dd1cf0363a79b5bef6b5/txn/flusher.go.fix_debugf	2018-07-05 13:36:04.000000000 +0200
+++ mgo-9856a29383ce1c59f308dd1cf0363a79b5bef6b5/txn/flusher.go	2019-06-03 18:31:11.248631076 +0200
@@ -576,7 +576,7 @@ func (f *flusher) assert(t *transaction,
 			continue
 		}
 		if op.Insert != nil {
-			return fmt.Errorf("Insert can only Assert txn.DocMissing", op.Assert)
+			return fmt.Errorf("Insert can only Assert txn.DocMissing: %v", op.Assert)
 		}
 		// if revnos[i] < 0 { abort }?