diff --git a/lightningd/invoice.c b/lightningd/invoice.c
index c8ffcb78a..0f10421f1 100644
--- a/lightningd/invoice.c
+++ b/lightningd/invoice.c
@@ -151,7 +151,7 @@ static void json_invoice(struct command *cmd,
 {
 	struct invoice invoice;
 	const struct invoice_details *details;
-	const jsmntok_t *msatoshi, *desctok, *fallbacks;
+	const jsmntok_t *desctok, *fallbacks;
 	const jsmntok_t *preimagetok;
 	u64 *msatoshi_val;
 	struct json_escaped *label_val, *desc;
@@ -165,7 +165,7 @@ static void json_invoice(struct command *cmd,
 	bool result;
 
 	if (!param(cmd, buffer, params,
-		   p_req("msatoshi", json_tok_tok, &msatoshi),
+		   p_req("msatoshi", json_tok_msat, &msatoshi_val),
 		   p_req("label", json_tok_label, &label_val),
 		   p_req("description", json_tok_tok, &desctok),
 		   p_opt_def("expiry", json_tok_u64, &expiry, 3600),
@@ -174,21 +174,6 @@ static void json_invoice(struct command *cmd,
 		   NULL))
 		return;
 
-	/* Get arguments. */
-	/* msatoshi */
-	if (json_tok_streq(buffer, msatoshi, "any"))
-		msatoshi_val = NULL;
-	else {
-		msatoshi_val = tal(cmd, u64);
-		if (!json_to_u64(buffer, msatoshi, msatoshi_val)
-		    || *msatoshi_val == 0) {
-			command_fail(cmd, JSONRPC2_INVALID_PARAMS,
-				     "'%.*s' is not a valid positive number",
-				     msatoshi->end - msatoshi->start,
-				     buffer + msatoshi->start);
-			return;
-		}
-	}
 	if (wallet_invoice_find_by_label(wallet, &invoice, label_val)) {
 		command_fail(cmd, INVOICE_LABEL_ALREADY_EXISTS,
 			     "Duplicate label '%s'", label_val->s);
diff --git a/lightningd/json.c b/lightningd/json.c
index 70ca770bb..2717f6355 100644
--- a/lightningd/json.c
+++ b/lightningd/json.c
@@ -159,6 +159,27 @@ bool json_tok_sha256(struct command *cmd, const char *name,
 	return false;
 }
 
+bool json_tok_msat(struct command *cmd, const char *name,
+		   const char *buffer, const jsmntok_t * tok,
+		   u64 **msatoshi_val)
+{
+	if (json_tok_streq(buffer, tok, "any")) {
+		*msatoshi_val = NULL;
+		return true;
+	}
+	*msatoshi_val = tal(cmd, u64);
+
+	if (json_to_u64(buffer, tok, *msatoshi_val) && *msatoshi_val != 0)
+		return true;
+
+	command_fail(cmd, JSONRPC2_INVALID_PARAMS,
+		     "'%s' should be a positive number or 'any', not '%.*s'",
+		     name,
+		     tok->end - tok->start,
+		     buffer + tok->start);
+	return false;
+}
+
 bool json_tok_percent(struct command *cmd, const char *name,
 		      const char *buffer, const jsmntok_t *tok,
 		      double **num)
diff --git a/lightningd/json.h b/lightningd/json.h
index 25f85a21e..9358110eb 100644
--- a/lightningd/json.h
+++ b/lightningd/json.h
@@ -63,6 +63,11 @@ bool json_tok_sha256(struct command *cmd, const char *name,
 		     const char *buffer, const jsmntok_t *tok,
 		     struct sha256 **hash);
 
+/* Extract positive integer, or NULL if tok is 'any'. */
+bool json_tok_msat(struct command *cmd, const char *name,
+		   const char *buffer, const jsmntok_t * tok,
+		   u64 **msatoshi_val);
+
 /* Extract double in range [0.0, 100.0] */
 bool json_tok_percent(struct command *cmd, const char *name,
 		      const char *buffer, const jsmntok_t *tok,
diff --git a/lightningd/test/run-param.c b/lightningd/test/run-param.c
index 79419eb3c..66f489c03 100644
--- a/lightningd/test/run-param.c
+++ b/lightningd/test/run-param.c
@@ -413,29 +413,6 @@ static void sendpay_nulltok(void)
 	assert(msatoshi == NULL);
 }
 
-static bool json_tok_msat(struct command *cmd,
-			  const char *name,
-			  const char *buffer,
-			  const jsmntok_t * tok,
-			  u64 **msatoshi_val)
-{
-	if (json_tok_streq(buffer, tok, "any")) {
-		*msatoshi_val = NULL;
-		return true;
-	}
-	*msatoshi_val = tal(cmd, u64);
-
-	if (json_to_u64(buffer, tok, *msatoshi_val) && *msatoshi_val != 0)
-		return true;
-
-	command_fail(cmd, JSONRPC2_INVALID_PARAMS,
-		     "'%s' should be a positive number or 'any', not '%.*s'",
-		     name,
-		     tok->end - tok->start,
-		     buffer + tok->start);
-	return false;
-}
-
 /*
  * New version of json_tok_label conforming to advanced style. This can eventually
  * replace the existing json_tok_label.