diff --git a/lib/nettle/int/rsa-keygen-fips186.c b/lib/nettle/int/rsa-keygen-fips186.c
index 624aa36..b064b45 100644
--- a/lib/nettle/int/rsa-keygen-fips186.c
+++ b/lib/nettle/int/rsa-keygen-fips186.c
@@ -27,7 +27,6 @@
 #include "config.h"
 #endif
 
-#include <assert.h>
 #include <stdlib.h>
 #include <stdio.h>
 #include <string.h>
@@ -337,10 +336,16 @@ _rsa_generate_fips186_4_keypair(struct rsa_public_key *pub,
 
 	mpz_mul(pub->n, key->p, key->q);
 
-	assert(mpz_sizeinbase(pub->n, 2) == n_size);
+	if (mpz_sizeinbase(pub->n, 2) != n_size) {
+		ret = 0;
+		goto cleanup;
+	}
 
 	/* c = q^{-1} (mod p) */
-	assert(mpz_invert(key->c, key->q, key->p) != 0);
+	if (mpz_invert(key->c, key->q, key->p) == 0) {
+		ret = 0;
+		goto cleanup;
+	}
 
 	mpz_sub_ui(p1, key->p, 1);
 	mpz_sub_ui(q1, key->q, 1);
@@ -352,6 +357,12 @@ _rsa_generate_fips186_4_keypair(struct rsa_public_key *pub,
 		goto cleanup;
 	}
 
+	/* check whether d > 2^(nlen/2) -- FIPS186-4 5.3.1 */
+	if (mpz_sizeinbase(key->d, 2) < n_size/2) {
+		ret = 0;
+		goto cleanup;
+	}
+
 	/* Done! Almost, we must compute the auxillary private values. */
 	/* a = d % (p-1) */
 	mpz_fdiv_r(key->a, key->d, p1);
@@ -362,7 +373,10 @@ _rsa_generate_fips186_4_keypair(struct rsa_public_key *pub,
 	/* c was computed earlier */
 
 	pub->size = key->size = (n_size + 7) / 8;
-	assert(pub->size >= RSA_MINIMUM_N_OCTETS);
+	if (pub->size < RSA_MINIMUM_N_OCTETS) {
+		ret = 0;
+		goto cleanup;
+	}
 
 	ret = 1;
  cleanup: