diff --git a/src/libraries/Common/tests/System/Security/Cryptography/X509Certificates/CertificateAuthority.cs b/src/libraries/Common/tests/System/Security/Cryptography/X509Certificates/CertificateAuthority.cs
index 00198a9ac853e3..360c4e36c41190 100644
--- a/src/libraries/Common/tests/System/Security/Cryptography/X509Certificates/CertificateAuthority.cs
+++ b/src/libraries/Common/tests/System/Security/Cryptography/X509Certificates/CertificateAuthority.cs
@@ -488,7 +488,7 @@ private byte[] BuildCrlManually(
 
             if (CorruptRevocationSignature)
             {
-                signature[5] ^= 0xFF;
+                signature[^2] ^= 0xFF;
             }
 
             // CertificateList
@@ -643,7 +643,7 @@ certs            [0] EXPLICIT SEQUENCE OF Certificate OPTIONAL }
 
                     if (CorruptRevocationSignature)
                     {
-                        signature[5] ^= 0xFF;
+                        signature[^2] ^= 0xFF;
                     }
 
                     writer.WriteBitString(signature);