diff --git a/internal/controllers/synthesis/slicecleanup.go b/internal/controllers/synthesis/slicecleanup.go
index ff3d1a98..562105e5 100644
--- a/internal/controllers/synthesis/slicecleanup.go
+++ b/internal/controllers/synthesis/slicecleanup.go
@@ -96,11 +96,20 @@ func shouldDeleteSlice(comp *apiv1.Composition, slice *apiv1.ResourceSlice) bool
 	if comp.Status.CurrentSynthesis == nil || slice.Spec.CompositionGeneration > comp.Status.CurrentSynthesis.ObservedCompositionGeneration {
 		return false // stale informer
 	}
-	isOutdated := slice.Spec.Attempt != 0 && comp.Status.CurrentSynthesis != nil && comp.Status.CurrentSynthesis.Attempts > slice.Spec.Attempt
-	isReferencedByComp := synthesisReferencesSlice(comp.Status.CurrentSynthesis, slice) || synthesisReferencesSlice(comp.Status.PreviousSynthesis, slice)
-	isSynthesized := comp.Status.CurrentSynthesis != nil && comp.Status.CurrentSynthesis.Synthesized != nil
-	compIsDeleted := comp.DeletionTimestamp != nil
-	return isOutdated || (isSynthesized && compIsDeleted || (!isReferencedByComp && slice.Spec.CompositionGeneration < comp.Generation))
+
+	var (
+		hasBeenRetried     = slice.Spec.Attempt != 0 && comp.Status.CurrentSynthesis.Attempts > slice.Spec.Attempt && slice.Spec.SynthesisUUID == comp.Status.CurrentSynthesis.UUID
+		isReferencedByComp = synthesisReferencesSlice(comp.Status.CurrentSynthesis, slice) || synthesisReferencesSlice(comp.Status.PreviousSynthesis, slice)
+		isSynthesized      = comp.Status.CurrentSynthesis.Synthesized != nil
+		compIsDeleted      = comp.DeletionTimestamp != nil
+		fromOldComposition = slice.Spec.CompositionGeneration < comp.Status.CurrentSynthesis.ObservedCompositionGeneration
+	)
+
+	// We can only safely delete resource slices when either:
+	// - Another retry of the same synthesis has already started
+	// - Synthesis is complete and the composition is being deleted
+	// - The slice was derived from an older composition
+	return hasBeenRetried || (isSynthesized && compIsDeleted) || (!isReferencedByComp && fromOldComposition)
 }
 
 func shouldReleaseSliceFinalizer(comp *apiv1.Composition, slice *apiv1.ResourceSlice) bool {
diff --git a/internal/controllers/synthesis/slicecleanup_test.go b/internal/controllers/synthesis/slicecleanup_test.go
index 9c9e4db9..f8906111 100644
--- a/internal/controllers/synthesis/slicecleanup_test.go
+++ b/internal/controllers/synthesis/slicecleanup_test.go
@@ -95,7 +95,30 @@ func TestShouldDeleteSlice(t *testing.T) {
 			expected: false,
 		},
 		{
-			name: "slice is outdated",
+			name: "another attempt started for a different synthesis, old one still references the slice",
+			comp: &apiv1.Composition{
+				Status: apiv1.CompositionStatus{
+					CurrentSynthesis: &apiv1.Synthesis{
+						Attempts: 5,
+						UUID:     "the-next-one",
+					},
+					PreviousSynthesis: &apiv1.Synthesis{
+						ResourceSlices: []*apiv1.ResourceSliceRef{{Name: "test-slice"}},
+					},
+				},
+			},
+			slice: &apiv1.ResourceSlice{
+				ObjectMeta: metav1.ObjectMeta{
+					Name: "test-slice",
+				},
+				Spec: apiv1.ResourceSliceSpec{
+					Attempt: 3,
+				},
+			},
+			expected: false,
+		},
+		{
+			name: "another attempt started for the same synthesis",
 			comp: &apiv1.Composition{
 				Status: apiv1.CompositionStatus{
 					CurrentSynthesis: &apiv1.Synthesis{
@@ -139,6 +162,162 @@ func TestShouldDeleteSlice(t *testing.T) {
 			slice:    &apiv1.ResourceSlice{},
 			expected: true,
 		},
+		{
+			name: "synthesis terminated and slice referenced",
+			comp: &apiv1.Composition{
+				Status: apiv1.CompositionStatus{
+					CurrentSynthesis: &apiv1.Synthesis{
+						Synthesized:    &metav1.Time{Time: time.Now()},
+						ResourceSlices: []*apiv1.ResourceSliceRef{{Name: "test-slice"}},
+					},
+				},
+			},
+			slice: &apiv1.ResourceSlice{
+				ObjectMeta: metav1.ObjectMeta{Name: "test-slice"},
+			},
+			expected: false,
+		},
+		{
+			name: "synthesis terminated, different composition generation, same synthesis",
+			comp: &apiv1.Composition{
+				Status: apiv1.CompositionStatus{
+					CurrentSynthesis: &apiv1.Synthesis{
+						Synthesized: &metav1.Time{Time: time.Now()},
+					},
+				},
+			},
+			slice: &apiv1.ResourceSlice{
+				ObjectMeta: metav1.ObjectMeta{Name: "test-slice"},
+				Spec: apiv1.ResourceSliceSpec{
+					CompositionGeneration: 2,
+				},
+			},
+			expected: false,
+		},
+		{
+			name: "synthesis terminated, same composition generation, different synthesis",
+			comp: &apiv1.Composition{
+				Status: apiv1.CompositionStatus{
+					CurrentSynthesis: &apiv1.Synthesis{
+						Synthesized: &metav1.Time{Time: time.Now()},
+					},
+				},
+			},
+			slice: &apiv1.ResourceSlice{
+				ObjectMeta: metav1.ObjectMeta{Name: "test-slice"},
+				Spec: apiv1.ResourceSliceSpec{
+					SynthesisUUID: "foo",
+				},
+			},
+			expected: false,
+		},
+		{
+			name: "synthesis terminated, newer composition generation, different synthesis",
+			comp: &apiv1.Composition{
+				ObjectMeta: metav1.ObjectMeta{
+					Generation: 3,
+				},
+				Status: apiv1.CompositionStatus{
+					CurrentSynthesis: &apiv1.Synthesis{
+						Synthesized:                   &metav1.Time{Time: time.Now()},
+						ObservedCompositionGeneration: 2,
+					},
+				},
+			},
+			slice: &apiv1.ResourceSlice{
+				ObjectMeta: metav1.ObjectMeta{Name: "test-slice"},
+				Spec: apiv1.ResourceSliceSpec{
+					SynthesisUUID:         "foo",
+					CompositionGeneration: 1,
+				},
+			},
+			expected: true,
+		},
+		{
+			name: "synthesis in-progress, newer composition generation, different synthesis",
+			comp: &apiv1.Composition{
+				ObjectMeta: metav1.ObjectMeta{
+					Generation: 3,
+				},
+				Status: apiv1.CompositionStatus{
+					CurrentSynthesis: &apiv1.Synthesis{
+						ObservedCompositionGeneration: 2,
+					},
+				},
+			},
+			slice: &apiv1.ResourceSlice{
+				ObjectMeta: metav1.ObjectMeta{Name: "test-slice"},
+				Spec: apiv1.ResourceSliceSpec{
+					SynthesisUUID:         "foo",
+					CompositionGeneration: 1,
+				},
+			},
+			expected: true,
+		},
+		{
+			name: "synthesis in-progress, newer composition generation, same synthesis",
+			comp: &apiv1.Composition{
+				ObjectMeta: metav1.ObjectMeta{
+					Generation: 2,
+				},
+				Status: apiv1.CompositionStatus{
+					CurrentSynthesis: &apiv1.Synthesis{
+						ObservedCompositionGeneration: 1,
+					},
+				},
+			},
+			slice: &apiv1.ResourceSlice{
+				ObjectMeta: metav1.ObjectMeta{Name: "test-slice"},
+				Spec: apiv1.ResourceSliceSpec{
+					CompositionGeneration: 1,
+				},
+			},
+			expected: false,
+		},
+		{
+			name: "synthesis terminated, newer composition and synthesis generation, different synthesis",
+			comp: &apiv1.Composition{
+				ObjectMeta: metav1.ObjectMeta{
+					Generation: 2,
+				},
+				Status: apiv1.CompositionStatus{
+					CurrentSynthesis: &apiv1.Synthesis{
+						Synthesized:                   &metav1.Time{Time: time.Now()},
+						ObservedCompositionGeneration: 2,
+					},
+				},
+			},
+			slice: &apiv1.ResourceSlice{
+				ObjectMeta: metav1.ObjectMeta{Name: "test-slice"},
+				Spec: apiv1.ResourceSliceSpec{
+					SynthesisUUID:         "foo",
+					CompositionGeneration: 1,
+				},
+			},
+			expected: true,
+		},
+		{
+			name: "synthesis terminated, older composition generation, different synthesis",
+			comp: &apiv1.Composition{
+				ObjectMeta: metav1.ObjectMeta{
+					Generation: 1,
+				},
+				Status: apiv1.CompositionStatus{
+					CurrentSynthesis: &apiv1.Synthesis{
+						Synthesized:                   &metav1.Time{Time: time.Now()},
+						ObservedCompositionGeneration: 1,
+					},
+				},
+			},
+			slice: &apiv1.ResourceSlice{
+				ObjectMeta: metav1.ObjectMeta{Name: "test-slice"},
+				Spec: apiv1.ResourceSliceSpec{
+					SynthesisUUID:         "foo",
+					CompositionGeneration: 2,
+				},
+			},
+			expected: false,
+		},
 		{
 			name: "composition is deleted but synthesis not terminated",
 			comp: &apiv1.Composition{