diff --git a/model/labels/labels_test.go b/model/labels/labels_test.go
index c497851d1..0221c66eb 100644
--- a/model/labels/labels_test.go
+++ b/model/labels/labels_test.go
@@ -708,7 +708,8 @@ func TestScratchBuilder(t *testing.T) {
 
 func TestLabels_Hash(t *testing.T) {
 	lbls := FromStrings("foo", "bar", "baz", "qux")
-	require.Equal(t, lbls.Hash(), lbls.Hash())
+	hash1, hash2 := lbls.Hash(), lbls.Hash()
+	require.Equal(t, hash1, hash2)
 	require.NotEqual(t, lbls.Hash(), FromStrings("foo", "bar").Hash(), "different labels match.")
 }
 
diff --git a/promql/engine.go b/promql/engine.go
index 02004e5f9..575ca58ea 100644
--- a/promql/engine.go
+++ b/promql/engine.go
@@ -1494,10 +1494,14 @@ func (ev *evaluator) eval(expr parser.Expr) (parser.Value, annotations.Annotatio
 						otherInArgs[j][0].F = otherArgs[j][0].Floats[step].F
 					}
 				}
-				maxt := ts - offset
-				mint := maxt - selRange
-				// Evaluate the matrix selector for this series for this step.
-				floats, histograms = ev.matrixIterSlice(it, mint, maxt, floats, histograms)
+				// Evaluate the matrix selector for this series
+				// for this step, but only if this is the 1st
+				// iteration or no @ modifier has been used.
+				if ts == ev.startTimestamp || selVS.Timestamp == nil {
+					maxt := ts - offset
+					mint := maxt - selRange
+					floats, histograms = ev.matrixIterSlice(it, mint, maxt, floats, histograms)
+				}
 				if len(floats)+len(histograms) == 0 {
 					continue
 				}
diff --git a/promql/testdata/functions.test b/promql/testdata/functions.test
index c40a6272b..4e104e406 100644
--- a/promql/testdata/functions.test
+++ b/promql/testdata/functions.test
@@ -221,19 +221,19 @@ eval instant at 50m deriv(testcounter_reset_middle[100m])
 # intercept at t=0: 6.818181818181818
 # intercept at t=3000: 38.63636363636364
 # intercept at t=3000+3600: 76.81818181818181
-eval instant at 50m predict_linear(testcounter_reset_middle[100m], 3600)
+eval instant at 50m predict_linear(testcounter_reset_middle[50m], 3600)
 	{} 76.81818181818181
 
 # intercept at t = 3000+3600 = 6600
-eval instant at 50m predict_linear(testcounter_reset_middle[100m] @ 3000, 3600)
+eval instant at 50m predict_linear(testcounter_reset_middle[50m] @ 3000, 3600)
 	{} 76.81818181818181
 
 # intercept at t = 600+3600 = 4200
-eval instant at 10m predict_linear(testcounter_reset_middle[100m] @ 3000, 3600)
+eval instant at 10m predict_linear(testcounter_reset_middle[50m] @ 3000, 3600)
 	{} 51.36363636363637
 
 # intercept at t = 4200+3600 = 7800
-eval instant at 70m predict_linear(testcounter_reset_middle[100m] @ 3000, 3600)
+eval instant at 70m predict_linear(testcounter_reset_middle[50m] @ 3000, 3600)
 	{} 89.54545454545455
 
 # With http_requests, there is a sample value exactly at the end of