diff --git a/common/iso4217.c b/common/iso4217.c
index 4238f6ced..f00ade86e 100644
--- a/common/iso4217.c
+++ b/common/iso4217.c
@@ -1,6 +1,6 @@
 #include <ccan/array_size/array_size.h>
+#include <ccan/mem/mem.h>
 #include <common/iso4217.h>
-#include <string.h>
 
 /* Wikipedia leads me to: https://www.currency-iso.org/en/home/tables/table-a1.html
 
@@ -191,10 +191,12 @@ static const struct iso4217_name_and_divisor iso4217[] = {
 	{ "ZWL", 2 },
 };
 
-const struct iso4217_name_and_divisor *find_iso4217(const char *prefix)
+const struct iso4217_name_and_divisor *find_iso4217(const utf8 *prefix,
+						    size_t len)
 {
 	for (size_t i = 0; i < ARRAY_SIZE(iso4217); i++) {
-		if (memcmp(iso4217[i].name, prefix, ISO4217_NAMELEN) == 0)
+		if (memeq(iso4217[i].name, strlen(iso4217[i].name),
+			  prefix, len))
 			return &iso4217[i];
 	}
 	return NULL;
diff --git a/common/iso4217.h b/common/iso4217.h
index aafe566c6..aca72b4b0 100644
--- a/common/iso4217.h
+++ b/common/iso4217.h
@@ -1,6 +1,7 @@
 #ifndef LIGHTNING_COMMON_ISO4217_H
 #define LIGHTNING_COMMON_ISO4217_H
 #include "config.h"
+#include <wire/wire.h>
 
 /* BOLT-offers #12:
  *
@@ -15,5 +16,6 @@ struct iso4217_name_and_divisor {
 
 #define ISO4217_NAMELEN 3
 
-const struct iso4217_name_and_divisor *find_iso4217(const char *prefix);
+const struct iso4217_name_and_divisor *find_iso4217(const utf8 *prefix,
+						    size_t len);
 #endif /* LIGHTNING_COMMON_ISO4217_H */
diff --git a/devtools/bolt12-cli.c b/devtools/bolt12-cli.c
index 8c336c235..b6ab3efdf 100644
--- a/devtools/bolt12-cli.c
+++ b/devtools/bolt12-cli.c
@@ -112,14 +112,14 @@ static bool print_amount(const struct bitcoin_blkid *chains,
 		minor_unit = 11;
 	} else {
 		const struct iso4217_name_and_divisor *iso;
-		currency = tal_strndup(tmpctx, iso4217, tal_bytelen(iso4217));
-		iso = find_iso4217(currency);
-		if (iso)
+		iso = find_iso4217(iso4217, tal_bytelen(iso4217));
+		if (iso) {
 			minor_unit = iso->minor_unit;
-		else {
+			currency = iso->name;
+		} else {
 			minor_unit = 0;
-			currency = tal_fmt(tmpctx, "%s (UNKNOWN CURRENCY)",
-					   currency);
+			currency = tal_fmt(tmpctx, "%.*s (UNKNOWN CURRENCY)",
+					   (int)tal_bytelen(iso4217), iso4217);
 			ok = false;
 		}
 	}