diff --git a/spdmlib/src/requester/encap_certificate.rs b/spdmlib/src/requester/encap_certificate.rs
index ed94281..0d379f6 100644
--- a/spdmlib/src/requester/encap_certificate.rs
+++ b/spdmlib/src/requester/encap_certificate.rs
@@ -101,7 +101,7 @@ impl RequesterContext {
         }
 
         let offset = get_certificate.offset;
-        if offset > my_cert_chain.data_size {
+        if offset >= my_cert_chain.data_size {
             self.encode_encap_error_response(
                 SpdmErrorCode::SpdmErrorInvalidRequest,
                 0,
diff --git a/spdmlib/src/responder/certificate_rsp.rs b/spdmlib/src/responder/certificate_rsp.rs
index 76c33ae..7a37a73 100644
--- a/spdmlib/src/responder/certificate_rsp.rs
+++ b/spdmlib/src/responder/certificate_rsp.rs
@@ -125,7 +125,7 @@ impl ResponderContext {
         }
 
         let offset = get_certificate.offset;
-        if offset > my_cert_chain.data_size {
+        if offset >= my_cert_chain.data_size {
             self.write_spdm_error(SpdmErrorCode::SpdmErrorInvalidRequest, 0, writer);
             return (
                 Err(SPDM_STATUS_INVALID_MSG_FIELD),