diff --git a/fw/hash.c b/fw/hash.c
index e962f0c..b876598 100644
--- a/fw/hash.c
+++ b/fw/hash.c
@@ -15,6 +15,8 @@
 #include <stdint.h>
 #include <string.h>
 
+#include <avr/pgmspace.h>
+
 #include "hash.h"
 
 
@@ -39,6 +41,19 @@ void hash_merge(const uint8_t *buf, uint8_t len)
 }
 
 
+#ifdef __AVR__
+
+void hash_merge_progmem(const uint8_t *buf, uint8_t len)
+{
+	uint8_t i;
+
+	for (i = 0; i != len; i++)
+		hash[i & (HASH_SIZE-1)] ^= pgm_read_byte(buf+i);
+}
+
+#endif /* __AVR__ */
+
+
 void hash_end(void)
 {
 }
diff --git a/fw/hash.h b/fw/hash.h
index 253b9db..bd20695 100644
--- a/fw/hash.h
+++ b/fw/hash.h
@@ -19,6 +19,7 @@
 
 void hash_init(void);
 void hash_merge(const uint8_t *buf, uint8_t len);
+void hash_merge_progmem(const uint8_t *buf, uint8_t len);
 void hash_end(void);
 bool hash_eq(const uint8_t *buf, uint8_t len, uint8_t off);
 void hash_cp(uint8_t *buf, uint8_t len, uint8_t off);