diff --git a/include/polarssl/rsa.h b/include/polarssl/rsa.h
index 629aa0f..513b037 100644
--- a/include/polarssl/rsa.h
+++ b/include/polarssl/rsa.h
@@ -114,6 +114,13 @@
         ASN1_STR_NULL "\x00"                    \
       ASN1_STR_OCTET_STRING "\x14"
 
+#define ASN1_HASH_SHA1_ALT                      \
+    ASN1_STR_CONSTRUCTED_SEQUENCE "\x1F"        \
+      ASN1_STR_CONSTRUCTED_SEQUENCE "\x07"      \
+        ASN1_STR_OID "\x05"                     \
+      OID_HASH_ALG_SHA1                         \
+      ASN1_STR_OCTET_STRING "\x14"
+
 #define ASN1_HASH_SHA2X                         \
     ASN1_STR_CONSTRUCTED_SEQUENCE "\x11"        \
       ASN1_STR_CONSTRUCTED_SEQUENCE "\x0d"      \