diff --git a/src/libopensc/card-isoApplet.c b/src/libopensc/card-isoApplet.c
index d3364cb1..8b39f914 100644
--- a/src/libopensc/card-isoApplet.c
+++ b/src/libopensc/card-isoApplet.c
@@ -1207,7 +1207,7 @@ isoApplet_compute_signature(struct sc_card *card,
 	if(drvdata->sec_env_alg_ref == ISOAPPLET_ALG_REF_ECDSA)
 	{
 		u8* p = NULL;
-		size_t len = drvdata->sec_env_ec_field_length / 4;
+		size_t len = (drvdata->sec_env_ec_field_length + 7) / 8 * 2;
 
 		if (len > outlen)
 			LOG_FUNC_RETURN(ctx, SC_ERROR_BUFFER_TOO_SMALL);
diff --git a/src/libopensc/card-myeid.c b/src/libopensc/card-myeid.c
index 63a35119..e8c28ec9 100644
--- a/src/libopensc/card-myeid.c
+++ b/src/libopensc/card-myeid.c
@@ -816,10 +816,10 @@ myeid_convert_ec_signature(struct sc_context *ctx, size_t s_len, unsigned char *
 	if (*data != 0x30 || *(data + 1) != (datalen - 2) || *(data + 2) != 0x02)
 		return SC_ERROR_INVALID_DATA;
 
-	buf = calloc(1, s_len/4);
+	buf = calloc(1, (s_len + 7)/8*2);
 	if (!buf)
 		LOG_FUNC_RETURN(ctx, SC_ERROR_OUT_OF_MEMORY);
-	buflen = s_len/4;
+	buflen = (s_len + 7)/8*2;
 
 	r = sc_asn1_sig_value_sequence_to_rs(ctx, data, datalen, buf, buflen);
         LOG_TEST_RET(ctx, r, "Failed to cenvert Sig-Value to the raw RS format");
diff --git a/src/libopensc/pkcs15-sec.c b/src/libopensc/pkcs15-sec.c
index 3b8764ff..3b3366b0 100644
--- a/src/libopensc/pkcs15-sec.c
+++ b/src/libopensc/pkcs15-sec.c
@@ -218,8 +218,8 @@ int sc_pkcs15_derive(struct sc_pkcs15_card *p15card,
 				LOG_FUNC_RETURN(ctx, SC_ERROR_NOT_SUPPORTED);
 			}
 
-			if (out == NULL || *poutlen < (prkey->field_length +7) / 8) {
-			    *poutlen = (prkey->field_length +7) / 8;
+			if (out == NULL || *poutlen < (prkey->field_length + 7) / 8) {
+			    *poutlen = (prkey->field_length + 7) / 8;
 			    r = 0; /* say no data to return */
 			    goto out;
 			}