diff --git a/keystore2/src/crypto/certificate_utils.cpp b/keystore2/src/crypto/certificate_utils.cpp
index 56dd3f4..500600f 100644
--- a/keystore2/src/crypto/certificate_utils.cpp
+++ b/keystore2/src/crypto/certificate_utils.cpp
@@ -537,7 +537,7 @@
     }
 
     uint8_t* cert_buf = nullptr;
-    size_t buf_len = i2d_re_X509_tbs(certificate, &cert_buf);
+    int buf_len = i2d_re_X509_tbs(certificate, &cert_buf);
     if (buf_len < 0) {
         return CertUtilsError::Encoding;
     }