diff --git a/metropolis/node/core/update/BUILD.bazel b/metropolis/node/core/update/BUILD.bazel
index e3cdcd1..e506984 100644
--- a/metropolis/node/core/update/BUILD.bazel
+++ b/metropolis/node/core/update/BUILD.bazel
@@ -1,4 +1,4 @@
-load("@io_bazel_rules_go//go:def.bzl", "go_library")
+load("@io_bazel_rules_go//go:def.bzl", "go_library", "go_test")
 
 go_library(
     name = "update",
@@ -18,3 +18,14 @@
         "@org_golang_x_sys//unix",
     ],
 )
+
+go_test(
+    name = "update_test",
+    srcs = ["update_test.go"],
+    embed = [":update"],
+    deps = [
+        "//metropolis/pkg/efivarfs",
+        "//metropolis/pkg/gpt",
+        "@com_github_google_uuid//:uuid",
+    ],
+)
diff --git a/metropolis/node/core/update/update.go b/metropolis/node/core/update/update.go
index 84a5db9..a357fa5 100644
--- a/metropolis/node/core/update/update.go
+++ b/metropolis/node/core/update/update.go
@@ -143,29 +143,9 @@
 }
 
 func (s *Service) getOrMakeBootEntry(existing map[int]*efivarfs.LoadOption, slot Slot) (int, error) {
-	for idx, e := range existing {
-		if len(e.FilePath) != 2 {
-			// Not our entry
-			continue
-		}
-		switch p := e.FilePath[0].(type) {
-		case *efivarfs.HardDrivePath:
-			gptMatch, ok := p.PartitionMatch.(*efivarfs.PartitionGPT)
-			if ok && gptMatch.PartitionUUID != s.ESPPart.ID {
-				// Not related to our ESP
-				continue
-			}
-		default:
-			continue
-		}
-		switch p := e.FilePath[1].(type) {
-		case efivarfs.FilePath:
-			if string(p) == slot.EFIBootPath() {
-				return idx, nil
-			}
-		default:
-			continue
-		}
+	idx, ok := s.findBootEntry(existing, slot)
+	if ok {
+		return idx, nil
 	}
 	newEntry := &efivarfs.LoadOption{
 		Description: fmt.Sprintf("Metropolis Slot %s", slot),
@@ -189,6 +169,34 @@
 	return newIdx, err
 }
 
+func (s *Service) findBootEntry(existing map[int]*efivarfs.LoadOption, slot Slot) (int, bool) {
+	for idx, e := range existing {
+		if len(e.FilePath) != 2 {
+			// Not our entry
+			continue
+		}
+		switch p := e.FilePath[0].(type) {
+		case *efivarfs.HardDrivePath:
+			gptMatch, ok := p.PartitionMatch.(efivarfs.PartitionGPT)
+			if !(ok && gptMatch.PartitionUUID == s.ESPPart.ID) {
+				// Not related to our ESP
+				continue
+			}
+		default:
+			continue
+		}
+		switch p := e.FilePath[1].(type) {
+		case efivarfs.FilePath:
+			if string(p) == slot.EFIBootPath() {
+				return idx, true
+			}
+		default:
+			continue
+		}
+	}
+	return 0, false
+}
+
 // MarkBootSuccessful must be called after each boot if some implementation-
 // defined criteria for a successful boot are met. If an update has been
 // installed and booted and this function is called, the updated version is
diff --git a/metropolis/node/core/update/update_test.go b/metropolis/node/core/update/update_test.go
new file mode 100644
index 0000000..8206a22
--- /dev/null
+++ b/metropolis/node/core/update/update_test.go
@@ -0,0 +1,127 @@
+package update
+
+import (
+	"testing"
+
+	"github.com/google/uuid"
+
+	"source.monogon.dev/metropolis/pkg/efivarfs"
+	"source.monogon.dev/metropolis/pkg/gpt"
+)
+
+func TestFindBootEntry(t *testing.T) {
+	testUUID1 := uuid.MustParse("85cb7a0c-d31d-4b65-1111-919b069915f1")
+	testUUID2 := uuid.MustParse("d3086aa2-0327-4634-2222-5c6c8488cae3")
+	cases := []struct {
+		name        string
+		slot        Slot
+		espid       uuid.UUID
+		entries     map[int]*efivarfs.LoadOption
+		expectedOk  bool
+		expectedIdx int
+	}{
+		{
+			name:       "NoEntries",
+			slot:       SlotA,
+			espid:      testUUID1,
+			entries:    make(map[int]*efivarfs.LoadOption),
+			expectedOk: false,
+		},
+		{
+			name:  "FindSimple",
+			slot:  SlotB,
+			espid: testUUID1,
+			entries: map[int]*efivarfs.LoadOption{
+				5: &efivarfs.LoadOption{
+					Description: "Other Entry",
+					FilePath: efivarfs.DevicePath{
+						&efivarfs.HardDrivePath{
+							PartitionNumber: 1,
+							PartitionMatch: efivarfs.PartitionMBR{
+								DiskSignature: [4]byte{1, 2, 3, 4},
+							},
+						},
+						efivarfs.FilePath("EFI/something/else.efi"),
+					},
+				},
+				6: &efivarfs.LoadOption{
+					Description: "Completely different entry",
+					FilePath: efivarfs.DevicePath{
+						&efivarfs.UnknownPath{
+							// Vendor-specific subtype
+							TypeVal:    1,
+							SubTypeVal: 4,
+							DataVal:    []byte{1, 2, 3, 4},
+						},
+						efivarfs.FilePath("EFI/something"),
+						efivarfs.FilePath("else.efi"),
+					},
+				},
+				16: &efivarfs.LoadOption{
+					Description: "Target Entry",
+					FilePath: efivarfs.DevicePath{
+						&efivarfs.HardDrivePath{
+							PartitionNumber: 2,
+							PartitionMatch: efivarfs.PartitionGPT{
+								PartitionUUID: testUUID1,
+							},
+						},
+						efivarfs.FilePath("/EFI/metropolis/boot-b.efi"),
+					},
+				},
+			},
+			expectedOk:  true,
+			expectedIdx: 16,
+		},
+		{
+			name:  "FindViaESPUUID",
+			slot:  SlotA,
+			espid: testUUID1,
+			entries: map[int]*efivarfs.LoadOption{
+				6: &efivarfs.LoadOption{
+					Description: "Other ESP UUID",
+					FilePath: efivarfs.DevicePath{
+						&efivarfs.HardDrivePath{
+							PartitionNumber: 2,
+							PartitionMatch: efivarfs.PartitionGPT{
+								PartitionUUID: testUUID2,
+							},
+						},
+						efivarfs.FilePath("/EFI/metropolis/boot-a.efi"),
+					},
+				},
+				7: &efivarfs.LoadOption{
+					Description: "Target Entry",
+					FilePath: efivarfs.DevicePath{
+						&efivarfs.HardDrivePath{
+							PartitionNumber: 2,
+							PartitionMatch: efivarfs.PartitionGPT{
+								PartitionUUID: testUUID1,
+							},
+						},
+						efivarfs.FilePath("/EFI/metropolis/boot-a.efi"),
+					},
+				},
+			},
+			expectedOk:  true,
+			expectedIdx: 7,
+		},
+	}
+
+	for _, c := range cases {
+		t.Run(c.name, func(t *testing.T) {
+			s := Service{
+				ESPPart: &gpt.Partition{
+					ID: c.espid,
+				},
+			}
+			idx, ok := s.findBootEntry(c.entries, c.slot)
+			if ok != c.expectedOk {
+				t.Fatalf("expected ok %t, got %t", c.expectedOk, ok)
+			}
+			if idx != c.expectedIdx {
+				t.Fatalf("expected idx %d, got %d", c.expectedIdx, idx)
+			}
+		})
+	}
+}