diff --git a/influxql/functions.go b/influxql/functions.go
index c49e322c19d..6f8571541f7 100644
--- a/influxql/functions.go
+++ b/influxql/functions.go
@@ -388,14 +388,14 @@ func MapStddev(itr Iterator) interface{} {
 }
 
 // ReduceStddev computes the stddev of values.
-func ReduceStddev(values []interface{}) interface{} {
+func ReduceStddev(values [][]float64) interface{} {
 	var data []float64
 	// Collect all the data points
 	for _, value := range values {
 		if value == nil {
 			continue
 		}
-		data = append(data, value.([]float64)...)
+		data = append(data, value...)
 	}
 
 	// If no data or we only have one point, it's nil or undefined