diff --git a/lib/src/interval/enharmonic_interval.dart b/lib/src/interval/enharmonic_interval.dart
index da683514..3340f2a5 100644
--- a/lib/src/interval/enharmonic_interval.dart
+++ b/lib/src/interval/enharmonic_interval.dart
@@ -3,40 +3,38 @@ part of '../../music_notes.dart';
 class EnharmonicInterval extends Enharmonic<Interval> {
   const EnharmonicInterval(super.semitones);
 
-  static const perfectUnison = EnharmonicInterval(1);
-  static const minorSecond = EnharmonicInterval(2);
-  static const majorSecond = EnharmonicInterval(3);
-  static const minorThird = EnharmonicInterval(4);
-  static const majorThird = EnharmonicInterval(5);
-  static const perfectFourth = EnharmonicInterval(6);
-  static const tritone = EnharmonicInterval(7);
-  static const perfectFifth = EnharmonicInterval(8);
-  static const minorSixth = EnharmonicInterval(9);
-  static const majorSixth = EnharmonicInterval(10);
-  static const minorSeventh = EnharmonicInterval(11);
-  static const majorSeventh = EnharmonicInterval(12);
+  static const perfectUnison = EnharmonicInterval(0);
+  static const minorSecond = EnharmonicInterval(1);
+  static const majorSecond = EnharmonicInterval(2);
+  static const minorThird = EnharmonicInterval(3);
+  static const majorThird = EnharmonicInterval(4);
+  static const perfectFourth = EnharmonicInterval(5);
+  static const tritone = EnharmonicInterval(6);
+  static const perfectFifth = EnharmonicInterval(7);
+  static const minorSixth = EnharmonicInterval(8);
+  static const majorSixth = EnharmonicInterval(9);
+  static const minorSeventh = EnharmonicInterval(10);
+  static const majorSeventh = EnharmonicInterval(11);
+  static const perfectOctave = EnharmonicInterval(12);
 
   @override
   Set<Interval> get items {
-    final interval = IntIntervalExtension.fromSemitones(semitones - 1);
+    final interval = IntIntervalExtension.fromSemitones(semitones);
 
     if (interval != null) {
-      final intervalBelow = interval == 1 ? 1 : interval - 1;
-      final intervalAbove = interval + 1;
-
       return SplayTreeSet<Interval>.of({
-        Interval.fromSemitones(intervalBelow, semitones - 1),
-        Interval.fromSemitones(interval, semitones - 1),
-        Interval.fromSemitones(intervalAbove, semitones - 1),
+        if (interval > 1) Interval.fromSemitones(interval - 1, semitones),
+        Interval.fromSemitones(interval, semitones),
+        Interval.fromSemitones(interval + 1, semitones),
       });
     }
 
-    final intervalBelow = IntIntervalExtension.fromSemitones(semitones - 2);
-    final intervalAbove = IntIntervalExtension.fromSemitones(semitones);
+    final intervalBelow = IntIntervalExtension.fromSemitones(semitones - 1);
+    final intervalAbove = IntIntervalExtension.fromSemitones(semitones + 1);
 
     return SplayTreeSet<Interval>.of({
-      Interval.fromSemitones(intervalBelow!, semitones - 1),
-      Interval.fromSemitones(intervalAbove!, semitones - 1),
+      Interval.fromSemitones(intervalBelow!, semitones),
+      Interval.fromSemitones(intervalAbove!, semitones),
     });
   }
 
diff --git a/test/src/enharmonic_test.dart b/test/src/enharmonic_test.dart
index 56dd931f..9cf618f4 100644
--- a/test/src/enharmonic_test.dart
+++ b/test/src/enharmonic_test.dart
@@ -9,9 +9,9 @@ void main() {
         expect(EnharmonicNote.g.toString(), '8 {F𝄪, G, A𝄫}');
         expect(EnharmonicNote.dSharp.toString(), '4 {D♯, E♭}');
 
-        expect(EnharmonicInterval.perfectUnison.toString(), '1 {P1, d2}');
-        expect(EnharmonicInterval.majorThird.toString(), '5 {M3, d4}');
-        expect(EnharmonicInterval.minorSixth.toString(), '9 {A5, m6, dd7}');
+        expect(EnharmonicInterval.perfectUnison.toString(), '0 {P1, d2}');
+        expect(EnharmonicInterval.majorThird.toString(), '4 {M3, d4}');
+        expect(EnharmonicInterval.minorSixth.toString(), '8 {A5, m6, dd7}');
       });
     });
   });
diff --git a/test/src/interval/enharmonic_interval_test.dart b/test/src/interval/enharmonic_interval_test.dart
index 6fa2d9b8..c8805c06 100644
--- a/test/src/interval/enharmonic_interval_test.dart
+++ b/test/src/interval/enharmonic_interval_test.dart
@@ -66,11 +66,16 @@ void main() {
             const Interval.imperfect(7, ImperfectQuality.major),
             const Interval.perfect(8, PerfectQuality.diminished),
           });
-          expect(const EnharmonicInterval(13).items, {
+          expect(EnharmonicInterval.perfectOctave.items, {
             const Interval.imperfect(7, ImperfectQuality.augmented),
             const Interval.perfect(8, PerfectQuality.perfect),
             const Interval.imperfect(9, ImperfectQuality.diminished),
           });
+          expect(const EnharmonicInterval(13).items, {
+            const Interval.perfect(8, PerfectQuality.augmented),
+            const Interval.imperfect(9, ImperfectQuality.minor),
+            const Interval.imperfect(10, ImperfectQuality.doubleDiminished),
+          });
         },
       );
     });
diff --git a/test/src/interval/interval_test.dart b/test/src/interval/interval_test.dart
index 7bf83bcc..c93e7a7c 100644
--- a/test/src/interval/interval_test.dart
+++ b/test/src/interval/interval_test.dart
@@ -129,26 +129,20 @@ void main() {
     group('.fromSemitonesQuality()', () {
       test('should return the correct Interval from semitones and Quality', () {
         expect(
-          Interval.fromSemitonesQuality(4),
-          equals(const Interval.imperfect(3, ImperfectQuality.minor)),
+          Interval.fromSemitonesQuality(3),
+          const Interval.imperfect(3, ImperfectQuality.minor),
         );
         expect(
-          Interval.fromSemitonesQuality(7),
-          equals(const Interval.perfect(4, PerfectQuality.augmented)),
+          Interval.fromSemitonesQuality(6),
+          const Interval.perfect(4, PerfectQuality.augmented),
         );
         expect(
-          Interval.fromSemitonesQuality(
-            7,
-            PerfectQuality.augmented,
-          ),
-          equals(const Interval.perfect(4, PerfectQuality.augmented)),
+          Interval.fromSemitonesQuality(6, PerfectQuality.augmented),
+          const Interval.perfect(4, PerfectQuality.augmented),
         );
         expect(
-          Interval.fromSemitonesQuality(
-            7,
-            PerfectQuality.diminished,
-          ),
-          equals(const Interval.perfect(5, PerfectQuality.diminished)),
+          Interval.fromSemitonesQuality(6, PerfectQuality.diminished),
+          const Interval.perfect(5, PerfectQuality.diminished),
         );
       });
     });
diff --git a/test/src/music_test.dart b/test/src/music_test.dart
index 411a5cab..aabe85b7 100644
--- a/test/src/music_test.dart
+++ b/test/src/music_test.dart
@@ -7,7 +7,7 @@ void main() {
       test('should return the correct chromatic scale notes', () {
         expect(
           chromaticScale,
-          equals(const [
+          const [
             EnharmonicNote.c,
             EnharmonicNote.cSharp,
             EnharmonicNote.d,
@@ -20,7 +20,7 @@ void main() {
             EnharmonicNote.a,
             EnharmonicNote.aSharp,
             EnharmonicNote.b,
-          ]),
+          ],
         );
       });
     });
diff --git a/test/src/note/note_test.dart b/test/src/note/note_test.dart
index bce38e64..a557fc7f 100644
--- a/test/src/note/note_test.dart
+++ b/test/src/note/note_test.dart
@@ -68,127 +68,113 @@ void main() {
       test('should return the Interval for a unison', () {
         expect(
           Note.c.exactInterval(Note.c),
-          equals(const Interval.perfect(1, PerfectQuality.perfect)),
+          const Interval.perfect(1, PerfectQuality.perfect),
         );
         expect(
           Note.c.exactInterval(Note.cSharp),
-          equals(const Interval.perfect(1, PerfectQuality.augmented)),
+          const Interval.perfect(1, PerfectQuality.augmented),
         );
       });
 
       test('should return the Interval for a second', () {
         expect(
           Note.c.exactInterval(const Note(Notes.d, Accidental.doubleFlat)),
-          equals(
-            const Interval.imperfect(2, ImperfectQuality.diminished),
-          ),
+          const Interval.imperfect(2, ImperfectQuality.diminished),
         );
         expect(
           Note.c.exactInterval(Note.dFlat),
-          equals(const Interval.imperfect(2, ImperfectQuality.minor)),
+          const Interval.imperfect(2, ImperfectQuality.minor),
         );
         expect(
           Note.c.exactInterval(Note.d),
-          equals(const Interval.imperfect(2, ImperfectQuality.major)),
+          const Interval.imperfect(2, ImperfectQuality.major),
         );
         expect(
           Note.c.exactInterval(Note.dSharp),
-          equals(
-            const Interval.imperfect(2, ImperfectQuality.augmented),
-          ),
+          const Interval.imperfect(2, ImperfectQuality.augmented),
         );
       });
 
       test('should return the Interval for a third', () {
         expect(
           Note.c.exactInterval(const Note(Notes.e, Accidental.doubleFlat)),
-          equals(
-            const Interval.imperfect(3, ImperfectQuality.diminished),
-          ),
+          const Interval.imperfect(3, ImperfectQuality.diminished),
         );
         expect(
           Note.c.exactInterval(Note.eFlat),
-          equals(const Interval.imperfect(3, ImperfectQuality.minor)),
+          const Interval.imperfect(3, ImperfectQuality.minor),
         );
         expect(
           Note.c.exactInterval(Note.e),
-          equals(const Interval.imperfect(3, ImperfectQuality.major)),
+          const Interval.imperfect(3, ImperfectQuality.major),
         );
         expect(
           Note.c.exactInterval(const Note(Notes.e, Accidental.sharp)),
-          equals(
-            const Interval.imperfect(3, ImperfectQuality.augmented),
-          ),
+          const Interval.imperfect(3, ImperfectQuality.augmented),
         );
       });
 
       test('should return the Interval for a fourth', () {
         expect(
           Note.c.exactInterval(const Note(Notes.f, Accidental.flat)),
-          equals(const Interval.perfect(4, PerfectQuality.diminished)),
+          const Interval.perfect(4, PerfectQuality.diminished),
         );
         expect(
           Note.c.exactInterval(Note.f),
-          equals(const Interval.perfect(4, PerfectQuality.perfect)),
+          const Interval.perfect(4, PerfectQuality.perfect),
         );
         expect(
           Note.c.exactInterval(Note.fSharp),
-          equals(const Interval.perfect(4, PerfectQuality.augmented)),
+          const Interval.perfect(4, PerfectQuality.augmented),
         );
       });
 
       test('should return the Interval for a fifth', () {
         expect(
           Note.c.exactInterval(Note.gFlat),
-          equals(const Interval.perfect(5, PerfectQuality.diminished)),
+          const Interval.perfect(5, PerfectQuality.diminished),
         );
         expect(
           Note.c.exactInterval(Note.g),
-          equals(const Interval.perfect(5, PerfectQuality.perfect)),
+          const Interval.perfect(5, PerfectQuality.perfect),
         );
         expect(
           Note.c.exactInterval(Note.gSharp),
-          equals(const Interval.perfect(5, PerfectQuality.augmented)),
+          const Interval.perfect(5, PerfectQuality.augmented),
         );
       });
 
       test('should return the Interval for a sixth', () {
         expect(
           Note.c.exactInterval(const Note(Notes.a, Accidental.doubleFlat)),
-          equals(
-            const Interval.imperfect(6, ImperfectQuality.diminished),
-          ),
+          const Interval.imperfect(6, ImperfectQuality.diminished),
         );
         expect(
           Note.c.exactInterval(Note.aFlat),
-          equals(const Interval.imperfect(6, ImperfectQuality.minor)),
+          const Interval.imperfect(6, ImperfectQuality.minor),
         );
         expect(
           Note.c.exactInterval(Note.a),
-          equals(const Interval.imperfect(6, ImperfectQuality.major)),
+          const Interval.imperfect(6, ImperfectQuality.major),
         );
         expect(
           Note.c.exactInterval(Note.aSharp),
-          equals(
-            const Interval.imperfect(6, ImperfectQuality.augmented),
-          ),
+          const Interval.imperfect(6, ImperfectQuality.augmented),
         );
       });
 
       test('should return the Interval for a seventh', () {
         expect(
           Note.c.exactInterval(const Note(Notes.b, Accidental.doubleFlat)),
-          equals(
-            const Interval.imperfect(7, ImperfectQuality.diminished),
-          ),
+          const Interval.imperfect(7, ImperfectQuality.diminished),
         );
         expect(
           Note.c.exactInterval(Note.bFlat),
-          equals(const Interval.imperfect(7, ImperfectQuality.minor)),
+          const Interval.imperfect(7, ImperfectQuality.minor),
         );
         expect(
           Note.c.exactInterval(Note.b),
-          equals(const Interval.imperfect(7, ImperfectQuality.major)),
+          const Interval.imperfect(7, ImperfectQuality.major),
         );
         // TODO(albertms10): add test case for:
         //  `Note.c.exactInterval(const Note(Notes.b, Accidental.sharp))`.