diff --git a/compliance/functions.json b/compliance/functions.json
index 8b8db36..2f48184 100644
--- a/compliance/functions.json
+++ b/compliance/functions.json
@@ -63,6 +63,10 @@
       "expression": "avg(numbers)",
       "result": 2.75
     },
+    {
+      "expression": "avg(empty_list)",
+      "result": null
+    },
     {
       "expression": "avg(array)",
       "error": "invalid-type"
diff --git a/functions.go b/functions.go
index e9770e8..64eb2a9 100644
--- a/functions.go
+++ b/functions.go
@@ -428,6 +428,10 @@ func jpfAvg(arguments []interface{}) (interface{}, error) {
 	// We've already type checked the value so we can safely use
 	// type assertions.
 	args := arguments[0].([]interface{})
+	// An empty array is null. The zero sum divided by zero was NaN.
+	if len(args) == 0 {
+		return nil, nil
+	}
 	length := float64(len(args))
 	numerator := 0.0
 	for _, n := range args {