diff --git a/include/mbedtls/bignum.h b/include/mbedtls/bignum.h
index d03b983..3c9eeea 100644
--- a/include/mbedtls/bignum.h
+++ b/include/mbedtls/bignum.h
@@ -299,7 +299,7 @@
  *
  * \param X        MPI to use
  */
-size_t mbedtls_mpi_msb( const mbedtls_mpi *X );
+size_t mbedtls_mpi_bitlen( const mbedtls_mpi *X );
 
 /**
  * \brief          Return the total size in bytes
diff --git a/include/mbedtls/compat-1.3.h b/include/mbedtls/compat-1.3.h
index 8b0342a..3c0f151 100644
--- a/include/mbedtls/compat-1.3.h
+++ b/include/mbedtls/compat-1.3.h
@@ -2149,7 +2149,7 @@
 #define mpi_lset mbedtls_mpi_lset
 #define mpi_mod_int mbedtls_mpi_mod_int
 #define mpi_mod_mpi mbedtls_mpi_mod_mpi
-#define mpi_msb mbedtls_mpi_msb
+#define mpi_msb mbedtls_mpi_bitlen
 #define mpi_mul_int mbedtls_mpi_mul_int
 #define mpi_mul_mpi mbedtls_mpi_mul_mpi
 #define mpi_read_binary mbedtls_mpi_read_binary