diff --git a/discover.go b/discover.go
index 2f8a02f..99fd392 100644
--- a/discover.go
+++ b/discover.go
@@ -172,7 +172,11 @@ func findDisks(disk, syspath string) (map[string][]partitionData, error) {
 			if err != nil {
 				return nil, err
 			}
-			end := size - start + 1
+			// sysfs reports `size` as the partition's length in sectors
+			// (not its last LBA), so the inclusive last sector is
+			// start + size - 1. The disk-image branch above uses the
+			// same formula.
+			end := start + size - 1
 			// read from uevent to get name
 			ueventPath := filepath.Join(sysClassBlockPath, candidate.Name(), name, "uevent")
 			ueventData, err := os.ReadFile(ueventPath)
diff --git a/discover_test.go b/discover_test.go
index 24fb180..edff615 100644
--- a/discover_test.go
+++ b/discover_test.go
@@ -133,11 +133,17 @@ func TestFindDisks(t *testing.T) {
 		if pd.label != "foo" {
 			t.Errorf("pd.label = %q, want foo", pd.label)
 		}
-		// start and size in bytes (blockSize=512)
+		// start, size, and end in bytes (blockSize=512). End is the
+		// inclusive last byte of the partition, i.e.
+		// (start_sector + size_sectors - 1) * blockSize.
 		if pd.start != 2*512 || pd.size != 4*512 {
 			t.Errorf("(start,size) = (%d,%d), want (%d,%d)",
 				pd.start, pd.size, 2*512, 4*512)
 		}
+		expectedEnd := int64((2+4-1) * 512)
+		if pd.end != expectedEnd {
+			t.Errorf("pd.end = %d, want %d", pd.end, expectedEnd)
+		}
 	})
 	t.Run("single", func(t *testing.T) {
 		// restrict to explicit disk