diff --git a/Assets/NuGet/Editor/NugetHelper.cs b/Assets/NuGet/Editor/NugetHelper.cs
index 630b27ef..a2314395 100644
--- a/Assets/NuGet/Editor/NugetHelper.cs
+++ b/Assets/NuGet/Editor/NugetHelper.cs
@@ -561,13 +561,26 @@ private static bool IsAlreadyImportedInEngine(NugetPackageIdentifier package)
         private static HashSet<string> alreadyImportedLibs = null;
         private static HashSet<string> GetAlreadyImportedLibs()
         {
+            
             if (alreadyImportedLibs == null)
             {
-                string[] lookupPaths = GetAllLookupPaths();
-                IEnumerable<string> libNames = lookupPaths
-                    .SelectMany(directory => Directory.EnumerateFiles(directory, "*.dll", SearchOption.AllDirectories))
-                    .Select(Path.GetFileName)
-                    .Select(p => Path.ChangeExtension(p, null));
+                // Find all the dll's already installed by NuGetForUnity
+                IList<string> nugetLibNames = new List<string>();
+
+                if (Directory.Exists(NugetConfigFile.RepositoryPath))
+                {
+                    nugetLibNames = Directory.EnumerateFiles(NugetConfigFile.RepositoryPath, "*.dll",
+                            SearchOption.AllDirectories)
+                        .Select(Path.GetFileName)
+                        .Select(p => Path.ChangeExtension(p, null))
+                        .ToList();
+                }
+
+                // Get a list of all assemblies loaded into Unity and filter out those installed by NuGetForUnity
+                List<string> libNames = AppDomain.CurrentDomain.GetAssemblies()
+                    .Select(a => a.ManifestModule.Name)
+                    .Select(p => Path.ChangeExtension(p, null))
+                    .Where(p => !nugetLibNames.Contains(p)).ToList();
                 alreadyImportedLibs = new HashSet<string>(libNames);
                 LogVerbose("Already imported libs: {0}", string.Join(", ", alreadyImportedLibs));
             }
@@ -575,29 +588,6 @@ private static HashSet<string> GetAlreadyImportedLibs()
             return alreadyImportedLibs;
         }
 
-        private static string[] GetAllLookupPaths()
-        {
-            var executablePath = EditorApplication.applicationPath;
-            var roots = new[] {
-                // MacOS directory layout
-                Path.Combine(executablePath, "Contents"),
-                // Windows directory layout
-                Path.Combine(Directory.GetParent(executablePath).FullName, "Data")
-            };
-            var relativePaths = new[] {
-                Path.Combine("NetStandard",  "compat"),
-                Path.Combine("MonoBleedingEdge", "lib", "mono")
-            };
-            var allPossiblePaths = roots
-                .SelectMany(root => relativePaths
-                    .Select(relativePath => Path.Combine(root, relativePath)));
-            var existingPaths = allPossiblePaths
-                .Where(Directory.Exists)
-                .ToArray();
-            LogVerbose("All existing path to dependency lookup are: {0}", string.Join(", ", existingPaths));
-            return existingPaths;
-        }
-
         public static NugetFrameworkGroup GetBestDependencyFrameworkGroupForCurrentSettings(NugetPackage package)
         {
             var targetFrameworks = package.Dependencies
diff --git a/Assets/Tests/Editor/NuGetTests.cs b/Assets/Tests/Editor/NuGetTests.cs
index 53e26596..1e368161 100644
--- a/Assets/Tests/Editor/NuGetTests.cs
+++ b/Assets/Tests/Editor/NuGetTests.cs
@@ -1,9 +1,8 @@
-using NUnit.Framework;
+using System.IO;
+using System.Reflection;
 using NugetForUnity;
-using System.IO;
-using System.Linq;
+using NUnit.Framework;
 using UnityEditor;
-using UnityEngine;
 
 public class NuGetTests
 {
@@ -222,4 +221,29 @@ public void PackageSourceCredentialsTest(string name)
         Assert.That(parsedSource.UserName, Is.EqualTo(username));
         Assert.That(parsedSource.SavedPassword, Is.EqualTo(password));
     }
+
+    [Test]
+    public void TestUpgrading()
+    {
+        NugetHelper.LoadNugetConfigFile();
+        
+        var componentModelAnnotation47 = new NugetPackageIdentifier("System.ComponentModel.Annotations", "4.7.0");
+        var componentModelAnnotation5 = new NugetPackageIdentifier("System.ComponentModel.Annotations", "5.0.0");
+        
+        NugetHelper.InstallIdentifier(componentModelAnnotation47);
+        Assert.IsTrue(NugetHelper.IsInstalled(componentModelAnnotation47), "The package was NOT installed: {0} {1}", componentModelAnnotation47.Id, componentModelAnnotation47.Version);
+
+        // Force NuGetHelper to reload the "alreadyImportedLibs"
+        var field = typeof(NugetHelper).GetField("alreadyImportedLibs", BindingFlags.Static | BindingFlags.NonPublic);
+        Assert.IsNotNull(field, "Failed to find the field 'alreadyImportedLibs' in NugetHelper");
+        field.SetValue(null, null);
+
+        NugetHelper.InstallIdentifier(componentModelAnnotation5);
+        Assert.IsTrue(NugetHelper.IsInstalled(componentModelAnnotation5), "The package was NOT installed: {0} {1}", componentModelAnnotation5.Id, componentModelAnnotation5.Version);
+        Assert.IsFalse(NugetHelper.IsInstalled(componentModelAnnotation47), "The package is STILL installed: {0} {1}", componentModelAnnotation47.Id, componentModelAnnotation47.Version);
+        
+        NugetHelper.UninstallAll();
+        
+        Assert.IsFalse(NugetHelper.IsInstalled(componentModelAnnotation5), "The package is STILL installed: {0} {1}", componentModelAnnotation5.Id, componentModelAnnotation5.Version);
+    }
 }