diff --git a/library/asn1write.c b/library/asn1write.c
index 13f4a39..626e0ff 100644
--- a/library/asn1write.c
+++ b/library/asn1write.c
@@ -109,7 +109,7 @@
         return( POLARSSL_ERR_ASN1_BUF_TOO_SMALL );
 
     (*p) -= len;
-    mpi_write_binary( X, *p, len );
+    MPI_CHK( mpi_write_binary( X, *p, len ) );
 
     // DER format assumes 2s complement for numbers, so the leftmost bit
     // should be 0 for positive numbers and 1 for negative numbers.
@@ -126,7 +126,10 @@
     ASN1_CHK_ADD( len, asn1_write_len( p, start, len ) );
     ASN1_CHK_ADD( len, asn1_write_tag( p, start, ASN1_INTEGER ) );
 
-    return( (int) len );
+    ret = (int) len;
+
+cleanup:
+    return( ret );
 }
 #endif /* POLARSSL_BIGNUM_C */