diff --git a/src/include/taler_amount_lib.h b/src/include/taler_amount_lib.h
index 72f5d4ffd..1f31e1498 100644
--- a/src/include/taler_amount_lib.h
+++ b/src/include/taler_amount_lib.h
@@ -99,7 +99,7 @@ TALER_string_to_amount (const char *str,
  * @return amount in network representation
  */
 struct TALER_AmountNBO
-TALER_amount_hton (struct TALER_Amount d);
+TALER_amount_hton (const struct TALER_Amount d);
 
 
 /**
@@ -109,7 +109,7 @@ TALER_amount_hton (struct TALER_Amount d);
  * @return amount in host representation
  */
 struct TALER_Amount
-TALER_amount_ntoh (struct TALER_AmountNBO dn);
+TALER_amount_ntoh (const struct TALER_AmountNBO dn);
 
 
 /**
diff --git a/src/util/amount.c b/src/util/amount.c
index cc0cdd6e3..9bdc0fd93 100644
--- a/src/util/amount.c
+++ b/src/util/amount.c
@@ -139,7 +139,7 @@ TALER_string_to_amount (const char *str,
  * FIXME
  */
 struct TALER_AmountNBO
-TALER_amount_hton (struct TALER_Amount d)
+TALER_amount_hton (const struct TALER_Amount d)
 {
   struct TALER_AmountNBO dn;
   dn.value = htonl (d.value);
@@ -154,7 +154,7 @@ TALER_amount_hton (struct TALER_Amount d)
  * FIXME
  */
 struct TALER_Amount
-TALER_amount_ntoh (struct TALER_AmountNBO dn)
+TALER_amount_ntoh (const struct TALER_AmountNBO dn)
 {
   struct TALER_Amount d;
   d.value = ntohl (dn.value);