diff --git a/promql/testdata/operators.test b/promql/testdata/operators.test
index d5a4d76f5..a6072eef3 100644
--- a/promql/testdata/operators.test
+++ b/promql/testdata/operators.test
@@ -467,3 +467,17 @@ eval instant at 5m test_total < bool test_smaller
     {instance="localhost"} 0
 
 eval instant at 5m test_total < test_smaller
+
+clear
+
+# Testing atan2.
+load 5m
+    trigy{} 10
+    trigx{} 20
+    trigNaN{} NaN
+
+eval instant at 5m trigy atan2 trigx
+    trigy{} 0.4636476090008061
+
+eval instant at 5m trigy atan2 trigNaN
+    trigy{} NaN