diff --git a/tf-psa-crypto/drivers/builtin/src/bignum_core.h b/tf-psa-crypto/drivers/builtin/src/bignum_core.h
index 1fc323ff9..69fa3063d 100644
--- a/tf-psa-crypto/drivers/builtin/src/bignum_core.h
+++ b/tf-psa-crypto/drivers/builtin/src/bignum_core.h
@@ -108,7 +108,7 @@
  *  }
  * not the other way round, in order to prevent misuse. (This is, if a value
  * other than the two below is passed, default to the safe path.) */
-#define MBEDTLS_MPI_IS_PUBLIC  0x2a2a
+#define MBEDTLS_MPI_IS_PUBLIC  0x2a2a2a2a
 #define MBEDTLS_MPI_IS_SECRET  0
 
 /** Count leading zero bits in a given integer.