diff --git a/src/libraries/System.Private.CoreLib/src/System/Diagnostics/Contracts/Contracts.cs b/src/libraries/System.Private.CoreLib/src/System/Diagnostics/Contracts/Contracts.cs
index 9840efd50cd1e9..49445f16b2d071 100644
--- a/src/libraries/System.Private.CoreLib/src/System/Diagnostics/Contracts/Contracts.cs
+++ b/src/libraries/System.Private.CoreLib/src/System/Diagnostics/Contracts/Contracts.cs
@@ -628,7 +628,7 @@ private static void AssertMustUseRewriter(ContractFailureKind kind, string contr
             Assembly? probablyNotRewritten = null;
             for (int i = 0; i < stack.FrameCount; i++)
             {
-                Assembly? caller = stack.GetFrame(i)!.GetMethod()?.DeclaringType!.Assembly;
+                Assembly? caller = stack.GetFrame(i)!.GetMethod()?.DeclaringType?.Assembly;
                 if (caller != null && caller != thisAssembly)
                 {
                     probablyNotRewritten = caller;