diff --git a/source/CreativeCoders.MacOS.HomeBrew/Models/Formulae/BrewFormulaModel.cs b/source/CreativeCoders.MacOS.HomeBrew/Models/Formulae/BrewFormulaModel.cs
index 1119e5c..da5c03c 100644
--- a/source/CreativeCoders.MacOS.HomeBrew/Models/Formulae/BrewFormulaModel.cs
+++ b/source/CreativeCoders.MacOS.HomeBrew/Models/Formulae/BrewFormulaModel.cs
@@ -65,7 +65,7 @@ public class BrewFormulaModel
 
     /// <summary>Gets or sets the compatibility version, if provided.</summary>
     [JsonPropertyName("compatibility_version")]
-    public string? CompatibilityVersion { get; set; }
+    public int? CompatibilityVersion { get; set; }
 
     /// <summary>Gets or sets whether autobump is enabled for the formula.</summary>
     [JsonPropertyName("autobump")]
diff --git a/tests/CreativeCoders.MacOS.HomeBrew.Tests/Models/Formulae/BrewFormulaModelTests.cs b/tests/CreativeCoders.MacOS.HomeBrew.Tests/Models/Formulae/BrewFormulaModelTests.cs
new file mode 100644
index 0000000..1784483
--- /dev/null
+++ b/tests/CreativeCoders.MacOS.HomeBrew.Tests/Models/Formulae/BrewFormulaModelTests.cs
@@ -0,0 +1,73 @@
+using System.Text.Json;
+using AwesomeAssertions;
+using CreativeCoders.MacOS.HomeBrew.Models;
+using CreativeCoders.MacOS.HomeBrew.Models.Formulae;
+
+namespace CreativeCoders.MacOS.HomeBrew.Tests.Models.Formulae;
+
+public class BrewFormulaModelTests
+{
+    [Fact]
+    public void Deserialize_WhenCompatibilityVersionIsNumber_ReturnsNumber()
+    {
+        // Arrange
+        const string json = """{"compatibility_version": 3}""";
+
+        // Act
+        var result = JsonSerializer.Deserialize<BrewFormulaModel>(json);
+
+        // Assert
+        result!.CompatibilityVersion.Should().Be(3);
+    }
+
+    [Fact]
+    public void Deserialize_WhenCompatibilityVersionIsNull_ReturnsNull()
+    {
+        // Arrange
+        const string json = """{"compatibility_version": null}""";
+
+        // Act
+        var result = JsonSerializer.Deserialize<BrewFormulaModel>(json);
+
+        // Assert
+        result!.CompatibilityVersion.Should().BeNull();
+    }
+
+    [Fact]
+    public void Deserialize_WhenCompatibilityVersionIsMissing_ReturnsNull()
+    {
+        // Arrange
+        const string json = """{}""";
+
+        // Act
+        var result = JsonSerializer.Deserialize<BrewFormulaModel>(json);
+
+        // Assert
+        result!.CompatibilityVersion.Should().BeNull();
+    }
+
+    [Fact]
+    public void Deserialize_WhenInstalledFormulaeHaveNumericCompatibilityVersion_ReturnsAllFormulae()
+    {
+        // Arrange
+        const string json = """
+            {
+                "formulae": [
+                    {"name": "abseil", "compatibility_version": 3},
+                    {"name": "wget", "compatibility_version": null}
+                ],
+                "casks": []
+            }
+            """;
+
+        // Act
+        var result = JsonSerializer.Deserialize<BrewInstalledModel>(json);
+
+        // Assert
+        result!.Formulae.Should().HaveCount(2);
+        result.Formulae[0].Name.Should().Be("abseil");
+        result.Formulae[0].CompatibilityVersion.Should().Be(3);
+        result.Formulae[1].Name.Should().Be("wget");
+        result.Formulae[1].CompatibilityVersion.Should().BeNull();
+    }
+}