diff --git a/lib/src/note/frequency.dart b/lib/src/note/frequency.dart
index a8857b87..8b922a58 100644
--- a/lib/src/note/frequency.dart
+++ b/lib/src/note/frequency.dart
@@ -7,7 +7,7 @@ class Frequency implements Comparable<Frequency> {
   final double hertz;
 
   /// Creates a new [Frequency] instance from [hertz].
-  const Frequency(this.hertz);
+  const Frequency(this.hertz) : assert(hertz >= 0, 'Hertz must be positive');
 
   /// The symbol for the Hertz unit.
   static const hertzUnitSymbol = 'Hz';
diff --git a/test/src/note/frequency_test.dart b/test/src/note/frequency_test.dart
index 7e91386f..b3284fb3 100644
--- a/test/src/note/frequency_test.dart
+++ b/test/src/note/frequency_test.dart
@@ -5,6 +5,12 @@ import 'package:test/test.dart';
 
 void main() {
   group('Frequency', () {
+    group('constructor', () {
+      test('should throw an assertion error when arguments are incorrect', () {
+        expect(() => Frequency(-0.1), throwsA(isA<AssertionError>()));
+      });
+    });
+
     group('.isHumanAudible', () {
       test('should return whether the frequency is audible by humans', () {
         expect(const Frequency(0).isHumanAudible, isFalse);