diff --git a/library/asn1write.c b/library/asn1write.c
index dd5a745..849e8c1 100644
--- a/library/asn1write.c
+++ b/library/asn1write.c
@@ -191,7 +191,7 @@
     if( *p - start < 1 )
         return( MBEDTLS_ERR_ASN1_BUF_TOO_SMALL );
 
-    *--(*p) = (boolean) ? 1 : 0;
+    *--(*p) = (boolean) ? 255 : 0;
     len++;
 
     MBEDTLS_ASN1_CHK_ADD( len, mbedtls_asn1_write_len( p, start, len ) );