diff --git a/library/ssl_cli.c b/library/ssl_cli.c
index 55a8e61..01e3f11 100644
--- a/library/ssl_cli.c
+++ b/library/ssl_cli.c
@@ -2610,6 +2610,7 @@
                                        unsigned char *end )
 {
     int ret = MBEDTLS_ERR_SSL_FEATURE_UNAVAILABLE;
+    size_t dhm_actual_bitlen;
 
     /*
      * Ephemeral DH parameters:
@@ -2627,10 +2628,11 @@
         return( ret );
     }
 
-    if( ssl->handshake->dhm_ctx.len * 8 < ssl->conf->dhm_min_bitlen )
+    dhm_actual_bitlen = mbedtls_mpi_bitlen( &ssl->handshake->dhm_ctx.P );
+    if( dhm_actual_bitlen < ssl->conf->dhm_min_bitlen )
     {
         MBEDTLS_SSL_DEBUG_MSG( 1, ( "DHM prime too short: %" MBEDTLS_PRINTF_SIZET " < %u",
-                                    ssl->handshake->dhm_ctx.len * 8,
+                                    dhm_actual_bitlen,
                                     ssl->conf->dhm_min_bitlen ) );
         return( MBEDTLS_ERR_SSL_BAD_HS_SERVER_KEY_EXCHANGE );
     }