diff --git a/tools/cache/delta_fifo.go b/tools/cache/delta_fifo.go
index f648673e..ea25122a 100644
--- a/tools/cache/delta_fifo.go
+++ b/tools/cache/delta_fifo.go
@@ -340,7 +340,7 @@ func (f *DeltaFIFO) AddIfNotPresent(obj interface{}) error {
 	if !ok {
 		return fmt.Errorf("object must be of type deltas, but got: %#v", obj)
 	}
-	id, err := f.KeyOf(deltas.Newest().Object)
+	id, err := f.KeyOf(deltas)
 	if err != nil {
 		return KeyError{obj, err}
 	}
diff --git a/tools/cache/delta_fifo_test.go b/tools/cache/delta_fifo_test.go
index ec4e4ff2..92247c4b 100644
--- a/tools/cache/delta_fifo_test.go
+++ b/tools/cache/delta_fifo_test.go
@@ -17,6 +17,7 @@ limitations under the License.
 package cache
 
 import (
+	"errors"
 	"fmt"
 	"reflect"
 	"runtime"
@@ -541,6 +542,11 @@ func TestDeltaFIFO_detectLineJumpers(t *testing.T) {
 func TestDeltaFIFO_addIfNotPresent(t *testing.T) {
 	f := NewDeltaFIFOWithOptions(DeltaFIFOOptions{KeyFunction: testFifoObjectKeyFunc})
 
+	emptyDeltas := Deltas{}
+	if err := f.AddIfNotPresent(emptyDeltas); err == nil || !errors.Is(err, ErrZeroLengthDeltasObject) {
+		t.Errorf("Expected error '%v', got %v", ErrZeroLengthDeltasObject, err)
+	}
+
 	f.Add(mkFifoObj("b", 3))
 	b3 := Pop(f)
 	f.Add(mkFifoObj("c", 4))