diff --git a/src/System.Private.CoreLib/Resources/Strings.resx b/src/System.Private.CoreLib/Resources/Strings.resx
index b13bce230d56..9ba8ed8837e8 100644
--- a/src/System.Private.CoreLib/Resources/Strings.resx
+++ b/src/System.Private.CoreLib/Resources/Strings.resx
@@ -2428,7 +2428,10 @@
   <data name="InvalidOperation_CannotImportGlobalFromDifferentModule" xml:space="preserve">
     <value>Unable to import a global method or field from a different module.</value>
   </data>
-  <data name="InvalidOperation_CannotRemoveLastFromEmptyCollection" xml:space="preserve">
+  <data name="InvalidOperation_CannotRegisterSecondResolver" xml:space="preserve">
+    <value>A Resolver is alerady Set for the Assembly.</value>
+  </data>
+    <data name="InvalidOperation_CannotRemoveLastFromEmptyCollection" xml:space="preserve">
     <value>Cannot remove the last element from an empty collection.</value>
   </data>
   <data name="InvalidOperation_CannotRestoreUnsupressedFlow" xml:space="preserve">
diff --git a/src/System.Private.CoreLib/src/System/Runtime/InteropServices/NativeLibrary.cs b/src/System.Private.CoreLib/src/System/Runtime/InteropServices/NativeLibrary.cs
index 6b24cd79eab7..e6cee1fbab7d 100644
--- a/src/System.Private.CoreLib/src/System/Runtime/InteropServices/NativeLibrary.cs
+++ b/src/System.Private.CoreLib/src/System/Runtime/InteropServices/NativeLibrary.cs
@@ -9,6 +9,7 @@
 using System.Runtime.ConstrainedExecution;
 using Win32Native = Microsoft.Win32.Win32Native;
 using System.Diagnostics;
+using System.Threading;
 
 namespace System.Runtime.InteropServices
 {
@@ -209,7 +210,8 @@ public static void SetDllImportResolver(Assembly assembly, DllImportResolver res
 
             if (s_nativeDllResolveMap == null)
             {
-                s_nativeDllResolveMap = new ConditionalWeakTable<Assembly, DllImportResolver>();
+                Interlocked.CompareExchange(ref s_nativeDllResolveMap,
+                    new ConditionalWeakTable<Assembly, DllImportResolver>(), null);
             }
 
             try
@@ -219,7 +221,7 @@ public static void SetDllImportResolver(Assembly assembly, DllImportResolver res
             catch (ArgumentException e)
             {
                 // ConditionalWealTable throws ArgumentException if the Key already exists
-                throw new InvalidOperationException("Resolver is alerady Set for the Assembly");
+                throw new InvalidOperationException(SR.InvalidOperation_CannotRegisterSecondResolver);
             }
         }
 
@@ -236,9 +238,12 @@ public static void SetDllImportResolver(Assembly assembly, DllImportResolver res
         internal static IntPtr LoadLibraryCallbackStub(string libraryName, Assembly assembly,
                                                        bool hasDllImportSearchPathFlags, uint dllImportSearchPathFlags)
         {
-            DllImportResolver resolver;
+            if (s_nativeDllResolveMap == null)
+            {
+                return IntPtr.Zero;
+            }
 
-            if (!s_nativeDllResolveMap.TryGetValue(assembly, out resolver))
+            if (!s_nativeDllResolveMap.TryGetValue(assembly, out DllImportResolver resolver))
             {
                 return IntPtr.Zero;
             }
diff --git a/tests/src/Interop/NativeLibraryResolveCallBack/CallBackTests.cs b/tests/src/Interop/NativeLibraryResolveCallBack/CallBackTests.cs
index 83deb6e49f03..67654203b4cd 100644
--- a/tests/src/Interop/NativeLibraryResolveCallBack/CallBackTests.cs
+++ b/tests/src/Interop/NativeLibraryResolveCallBack/CallBackTests.cs
@@ -27,19 +27,27 @@ public static int Main()
                         throw new ArgumentException();
                     }
 
-                    return NativeLibrary.Load("ResolveLib", asm, dllImportSearchPath);
+                    return NativeLibrary.Load("ResolveLib", asm, null);
                 };
 
             DllImportResolver anotherResolver =
                 (string libraryName, Assembly asm, DllImportSearchPath? dllImportSearchPath) =>
                     IntPtr.Zero;
 
+            try
+            {
+                NativeSum(10, 10);
+                Console.WriteLine("Exception expected: no callback registered yet");
+                return 101;
+            }
+            catch (DllNotFoundException e) {}
+
             try
             {
                 NativeLibrary.SetDllImportResolver(null, resolver);
 
-                Console.WriteLine("Expected exception not thrown");
-                return 101;
+                Console.WriteLine("Exception expected: assembly parameter null");
+                return 102;
             }
             catch (ArgumentNullException e) { }
 
@@ -47,8 +55,8 @@ public static int Main()
             {
                 NativeLibrary.SetDllImportResolver(assembly, null);
 
-                Console.WriteLine("Expected exception not thrown");
-                return 102;
+                Console.WriteLine("Exception expected: resolver parameter null");
+                return 103;
             }
             catch (ArgumentNullException e) { }
 
@@ -60,21 +68,21 @@ public static int Main()
                 // Try to set another resolver on the same assembly.
                 NativeLibrary.SetDllImportResolver(assembly, anotherResolver);
 
-                Console.WriteLine("Expected Exception not thrown");
-                return 103;
+                Console.WriteLine("Exception expected: Trying to register second resolver");
+                return 104;
             }
             catch (InvalidOperationException e) { }
 
             if (NativeSum(10, 10) != 20)
             {
                 Console.WriteLine("Unexpected ReturnValue from NativeSum()");
-                return 104;
+                return 105;
             }
         }
         catch (Exception e)
         {
             Console.WriteLine($"Unexpected exception: {e.ToString()} {e.Message}");
-            return 105;
+            return 106;
         }
 
         return 100;