diff --git a/src/libraries/Common/src/Interop/Interop.Ldap.cs b/src/libraries/Common/src/Interop/Interop.Ldap.cs
index d933cf98f2ed1c..0fbb469302b8ba 100644
--- a/src/libraries/Common/src/Interop/Interop.Ldap.cs
+++ b/src/libraries/Common/src/Interop/Interop.Ldap.cs
@@ -268,7 +268,7 @@ public void Free() {}
             }
         }
 #else
-        public static readonly unsafe int Size = Marshal.SizeOf<LdapReferralCallback>();
+        public static readonly unsafe int Size = sizeof(LdapReferralCallback);
 #endif
     }
 
diff --git a/src/libraries/Common/src/Interop/Windows/Advapi32/Interop.LsaLookupSids.cs b/src/libraries/Common/src/Interop/Windows/Advapi32/Interop.LsaLookupSids.cs
index 24abe5323e5bd4..305cbdfd250f1c 100644
--- a/src/libraries/Common/src/Interop/Windows/Advapi32/Interop.LsaLookupSids.cs
+++ b/src/libraries/Common/src/Interop/Windows/Advapi32/Interop.LsaLookupSids.cs
@@ -27,7 +27,7 @@ public static unsafe void InitializeReferencedDomainsList(this SafeLsaMemoryHand
         // We don't know the real size of the referenced domains yet, so we need to set an initial
         // size based on the LSA_REFERENCED_DOMAIN_LIST structure, then resize it to include all of
         // the domains.
-        referencedDomains.Initialize((uint)Marshal.SizeOf<Interop.LSA_REFERENCED_DOMAIN_LIST>());
+        referencedDomains.Initialize((ulong)sizeof(Interop.LSA_REFERENCED_DOMAIN_LIST));
         Interop.LSA_REFERENCED_DOMAIN_LIST domainList = referencedDomains.Read<Interop.LSA_REFERENCED_DOMAIN_LIST>(0);
 
         byte* pRdl = null;
diff --git a/src/libraries/System.DirectoryServices.Protocols/src/System/DirectoryServices/Protocols/Interop/LdapPal.Linux.cs b/src/libraries/System.DirectoryServices.Protocols/src/System/DirectoryServices/Protocols/Interop/LdapPal.Linux.cs
index 15b3cd86effafb..ab965f9fefaab6 100644
--- a/src/libraries/System.DirectoryServices.Protocols/src/System/DirectoryServices/Protocols/Interop/LdapPal.Linux.cs
+++ b/src/libraries/System.DirectoryServices.Protocols/src/System/DirectoryServices/Protocols/Interop/LdapPal.Linux.cs
@@ -226,7 +226,7 @@ internal static int SaslInteractionProcedure(IntPtr ldapHandle, uint flags, IntP
 
                 // Move to next interact challenge
                 Marshal.StructureToPtr(interactChallenge, currentInteractPtr, false);
-                currentInteractPtr = IntPtr.Add(currentInteractPtr, Marshal.SizeOf<SaslInteractiveChallenge>());
+                currentInteractPtr = IntPtr.Add(currentInteractPtr, sizeof(SaslInteractiveChallenge));
                 interactChallenge = Marshal.PtrToStructure<SaslInteractiveChallenge>(currentInteractPtr);
             }