diff --git a/include/polarssl/asn1write.h b/include/polarssl/asn1write.h
index 6e4a25798..9b98afe2e 100644
--- a/include/polarssl/asn1write.h
+++ b/include/polarssl/asn1write.h
@@ -52,6 +52,8 @@ int asn1_write_bitstring( unsigned char **p, unsigned char *start,
                           const unsigned char *buf, size_t bits );
 int asn1_write_octet_string( unsigned char **p, unsigned char *start,
                              const unsigned char *buf, size_t size );
+int asn1_write_raw_buffer( unsigned char **p, unsigned char *start,
+                           const unsigned char *buf, size_t size );
 
 #ifdef __cplusplus
 }
diff --git a/library/asn1write.c b/library/asn1write.c
index fc85bf990..f08e105d2 100644
--- a/library/asn1write.c
+++ b/library/asn1write.c
@@ -272,7 +272,7 @@ int asn1_write_octet_string( unsigned char **p, unsigned char *start,
     int ret;
     size_t len = 0;
 
-    if( *p - start < (int) size + 1 )
+    if( *p - start < (int) size )
         return( POLARSSL_ERR_ASN1_BUF_TOO_SMALL );
 
     len = size;
@@ -285,4 +285,19 @@ int asn1_write_octet_string( unsigned char **p, unsigned char *start,
     return( len );
 }
 
+int asn1_write_raw_buffer( unsigned char **p, unsigned char *start,
+                           const unsigned char *buf, size_t size )
+{
+    size_t len = 0;
+
+    if( *p - start < (int) size )
+        return( POLARSSL_ERR_ASN1_BUF_TOO_SMALL );
+
+    len = size;
+    (*p) -= len;
+    memcpy( *p, buf, len );
+
+    return( len );
+}
+
 #endif