diff --git a/src/System.IO.Abstractions.TestingHelpers/MockDirectory.cs b/src/System.IO.Abstractions.TestingHelpers/MockDirectory.cs
index 39eb41947..bc845c1e1 100644
--- a/src/System.IO.Abstractions.TestingHelpers/MockDirectory.cs
+++ b/src/System.IO.Abstractions.TestingHelpers/MockDirectory.cs
@@ -177,7 +177,7 @@ public override string[] GetDirectories(string path, string searchPattern, Searc
 #if FEATURE_ENUMERATION_OPTIONS
         public override string[] GetDirectories(string path, string searchPattern, EnumerationOptions enumerationOptions)
         {
-            return GetDirectories(path, "*", enumerationOptions.RecurseSubdirectories ? SearchOption.AllDirectories : SearchOption.TopDirectoryOnly);
+            return GetDirectories(path, "*", EnumerationOptionsToSearchOption(enumerationOptions));
         }
 #endif
 
@@ -206,7 +206,7 @@ public override string[] GetFiles(string path, string searchPattern, SearchOptio
 #if FEATURE_ENUMERATION_OPTIONS
         public override string[] GetFiles(string path, string searchPattern, EnumerationOptions enumerationOptions)
         {
-            return GetFiles(path, "*", enumerationOptions.RecurseSubdirectories ? SearchOption.AllDirectories : SearchOption.TopDirectoryOnly);
+            return GetFiles(path, "*", EnumerationOptionsToSearchOption(enumerationOptions));
         }
 #endif
 
@@ -638,5 +638,42 @@ private string ReplaceLastOccurrence(string source, string find, string replace)
             var result = source.Remove(place, find.Length).Insert(place, replace);
             return result;
         }
+
+#if FEATURE_ENUMERATION_OPTIONS
+        private SearchOption EnumerationOptionsToSearchOption(EnumerationOptions enumerationOptions)
+        {
+            static Exception CreateExceptionForUnsupportedProperty(string propertyName)
+            {
+                return new NotSupportedException(
+                    $"Changing EnumerationOptions.{propertyName} is not yet implemented for the mock file system."
+                );
+            }
+
+            if (enumerationOptions.AttributesToSkip != (FileAttributes.System | FileAttributes.Hidden))
+            {
+                throw CreateExceptionForUnsupportedProperty("AttributesToSkip");
+            }
+            if (!enumerationOptions.IgnoreInaccessible)
+            {
+                throw CreateExceptionForUnsupportedProperty("IgnoreInaccessible");
+            }
+            if (enumerationOptions.MatchCasing != MatchCasing.PlatformDefault)
+            {
+                throw CreateExceptionForUnsupportedProperty("MatchCasing");
+            }
+            if (enumerationOptions.MatchType != MatchType.Simple)
+            {
+                throw CreateExceptionForUnsupportedProperty("MatchType");
+            }
+            if (enumerationOptions.ReturnSpecialDirectories)
+            {
+                throw CreateExceptionForUnsupportedProperty("ReturnSpecialDirectories");
+            }
+
+            return enumerationOptions.RecurseSubdirectories
+                ? SearchOption.AllDirectories
+                : SearchOption.TopDirectoryOnly;
+        }
+#endif
     }
 }
diff --git a/src/System.IO.Abstractions.TestingHelpers/System.IO.Abstractions.TestingHelpers.csproj b/src/System.IO.Abstractions.TestingHelpers/System.IO.Abstractions.TestingHelpers.csproj
index 819264659..ce27c683d 100644
--- a/src/System.IO.Abstractions.TestingHelpers/System.IO.Abstractions.TestingHelpers.csproj
+++ b/src/System.IO.Abstractions.TestingHelpers/System.IO.Abstractions.TestingHelpers.csproj
@@ -3,7 +3,7 @@
         <AssemblyName>System.IO.Abstractions.TestingHelpers</AssemblyName>
         <RootNamespace>System.IO.Abstractions.TestingHelpers</RootNamespace>
         <Description>A set of pre-built mocks to help when testing file system interactions.</Description>
-        <TargetFrameworks>netstandard2.0;netstandard2.1;net461</TargetFrameworks>
+        <TargetFrameworks>netstandard2.1;netstandard2.0;net461</TargetFrameworks>
         <PackageProjectUrl>https://github.com/System-IO-Abstractions/System.IO.Abstractions</PackageProjectUrl>
         <PackageLicenseExpression>MIT</PackageLicenseExpression>
         <PackageTags>testing</PackageTags>
diff --git a/tests/System.IO.Abstractions.TestingHelpers.Tests/System.IO.Abstractions.TestingHelpers.Tests.csproj b/tests/System.IO.Abstractions.TestingHelpers.Tests/System.IO.Abstractions.TestingHelpers.Tests.csproj
index 2f195e99f..53c87c6a7 100644
--- a/tests/System.IO.Abstractions.TestingHelpers.Tests/System.IO.Abstractions.TestingHelpers.Tests.csproj
+++ b/tests/System.IO.Abstractions.TestingHelpers.Tests/System.IO.Abstractions.TestingHelpers.Tests.csproj
@@ -1,6 +1,6 @@
 <Project Sdk="Microsoft.NET.Sdk">
   <PropertyGroup>
-    <TargetFrameworks>netcoreapp2.1;netcoreapp3.0</TargetFrameworks>
+    <TargetFrameworks>netcoreapp3.0;netcoreapp2.1</TargetFrameworks>
     <TargetFrameworks Condition="!$([MSBuild]::IsOsUnixLike())">$(TargetFrameworks);net461</TargetFrameworks>
     <Description>The unit tests for our pre-built mocks</Description>
     <AssemblyName>System.IO.Abstractions.TestingHelpers.Tests</AssemblyName>