diff --git a/docs/querying/operators.md b/docs/querying/operators.md
index 714b41b3c3..9f35e0c153 100644
--- a/docs/querying/operators.md
+++ b/docs/querying/operators.md
@@ -241,7 +241,7 @@ vector. `by` and `without` are only used to bucket the input vector.
 `quantile` calculates the φ-quantile, the value that ranks at number φ*N among
 the N metric values of the dimensions aggregated over. φ is provided as the
 aggregation parameter. For example, `quantile(0.5, ...)` calculates the median,
-`quantile(0.95, ...)` the 95th percentile. For φ = `NaN`, `NaN` is returned. 
+`quantile(0.95, ...)` the 95th percentile. For φ = `NaN`, `NaN` is returned. For φ < 0, `-Inf` is returned. For φ > 1, `+Inf` is returned.
 
 Example:
 
diff --git a/promql/quantile.go b/promql/quantile.go
index 26dcf81d2c..a3abf68dd0 100644
--- a/promql/quantile.go
+++ b/promql/quantile.go
@@ -186,7 +186,7 @@ func ensureMonotonic(buckets buckets) {
 // quantile calculates the given quantile of a vector of samples.
 //
 // The Vector will be sorted.
-// If 'values' has zero elements
+// If 'values' has zero elements, NaN is returned.
 // If q==NaN, NaN is returned.
 // If q<0, -Inf is returned.
 // If q>1, +Inf is returned.
diff --git a/promql/testdata/aggregators.test b/promql/testdata/aggregators.test
index 220c5edce1..8709b393b2 100644
--- a/promql/testdata/aggregators.test
+++ b/promql/testdata/aggregators.test
@@ -399,6 +399,11 @@ eval instant at 1m quantile without(point)((scalar(foo)), data)
 	{test="three samples"} 1.6
 	{test="uneven samples"} 2.8
 
+eval instant at 1m quantile without(point)(NaN, data)
+    {test="two samples"} NaN
+    {test="three samples"} NaN
+    {test="uneven samples"} NaN
+
 # Tests for group.
 clear