diff --git a/src/libraries/Fuzzing/DotnetFuzzing/Fuzzers/AssemblyNameInfoFuzzer.cs b/src/libraries/Fuzzing/DotnetFuzzing/Fuzzers/AssemblyNameInfoFuzzer.cs
index 32b7e8a2ff1b19..0fbc20941513e4 100644
--- a/src/libraries/Fuzzing/DotnetFuzzing/Fuzzers/AssemblyNameInfoFuzzer.cs
+++ b/src/libraries/Fuzzing/DotnetFuzzing/Fuzzers/AssemblyNameInfoFuzzer.cs
@@ -68,11 +68,13 @@ private static void Test(Span<char> span)
                     // When converting to AssemblyName, the culture name is lower-cased
                     // by the CultureInfo ctor that calls CultureData.GetCultureData
                     // which lowers the name for caching and normalization purposes.
+                    // It lowers only the part before the `-` character, but we lower
+                    // the whole string for the sake of simplicity of this test.
 
                     string lowerCase = fromTryParse.CultureName.ToLower();
                     if (lowerCase != "c")
                     {
-                        Assert.Equal(lowerCase, fromParse.ToAssemblyName().CultureName);
+                        Assert.Equal(lowerCase, fromParse.ToAssemblyName().CultureName!.ToLower());
                     }
                     else
                     {
diff --git a/src/libraries/System.Reflection.Metadata/tests/Metadata/AssemblyNameInfoTests.cs b/src/libraries/System.Reflection.Metadata/tests/Metadata/AssemblyNameInfoTests.cs
index d399f5582390cf..05db85d2f1d14c 100644
--- a/src/libraries/System.Reflection.Metadata/tests/Metadata/AssemblyNameInfoTests.cs
+++ b/src/libraries/System.Reflection.Metadata/tests/Metadata/AssemblyNameInfoTests.cs
@@ -1,6 +1,7 @@
 // Licensed to the .NET Foundation under one or more agreements.
 // The .NET Foundation licenses this file to you under the MIT license.
 
+using System.Collections.Generic;
 using System.Globalization;
 using Xunit;
 
@@ -106,15 +107,24 @@ public void EmptyInputIsInvalid()
             Assert.Throws<ArgumentException>(() => AssemblyNameInfo.Parse("".AsSpan()));
         }
 
-        [Fact]
-        public void CultureNameGetLoweredByToAssemblyName()
+
+        public static IEnumerable<object[]> CultureNameGetLoweredByToAssemblyName_Arguments()
+        {
+            yield return new object[] { "aA", "aa" };
+            yield return new object[] { "B-BB", PlatformDetection.IsNetFramework ? "B-BB" : "b-BB" };
+        }
+
+        [ConditionalTheory(typeof(PlatformDetection), nameof(PlatformDetection.IsNotWindowsNanoServer))]
+        [MemberData(nameof(CultureNameGetLoweredByToAssemblyName_Arguments))]
+        public void CultureNameGetLoweredByToAssemblyName(string input, string expected)
         {
-            AssemblyNameInfo assemblyNameInfo = AssemblyNameInfo.Parse("test,culture=aA".AsSpan());
-            Assert.Equal("aA", assemblyNameInfo.CultureName);
+            AssemblyNameInfo assemblyNameInfo = AssemblyNameInfo.Parse($"test,culture={input}".AsSpan());
+            Assert.Equal(input, assemblyNameInfo.CultureName);
             // When converting to AssemblyName, the culture name is lower-cased
             // by the CultureInfo ctor that calls CultureData.GetCultureData
             // which lowers the name for caching and normalization purposes.
-            Assert.Equal("aa", assemblyNameInfo.ToAssemblyName().CultureName);
+            // It lowers only the part before the `-` character.
+            Assert.Equal(expected, assemblyNameInfo.ToAssemblyName().CultureName);
         }
 
         [Theory]