diff --git a/library/dhm.c b/library/dhm.c
index 6fa5435..535b698 100644
--- a/library/dhm.c
+++ b/library/dhm.c
@@ -263,7 +263,8 @@
         goto cleanup;
 
     /*
-     * export P, G, GX
+     * Export P, G, GX. RFC 5246 §4.4 states that "leading zero octets are
+     * not required". We omit leading zeros for compactness.
      */
 #define DHM_MPI_EXPORT( X, n )                                          \
     do {                                                                \
@@ -477,8 +478,9 @@
         MBEDTLS_MPI_CHK( mbedtls_mpi_mod_mpi( &ctx->K, &ctx->K, &ctx->P ) );
     }
 
+    /* Output the secret without any leading zero byte. This is mandatory
+     * for TLS per RFC 5246 §8.1.2. */
     *olen = mbedtls_mpi_size( &ctx->K );
-
     MBEDTLS_MPI_CHK( mbedtls_mpi_write_binary( &ctx->K, output, *olen ) );
 
 cleanup: