diff --git a/libpromises/evalfunction.c b/libpromises/evalfunction.c
index 8dfcdc8e42..ed5f8627da 100644
--- a/libpromises/evalfunction.c
+++ b/libpromises/evalfunction.c
@@ -11541,6 +11541,8 @@ static const FnCallArg DATA_EXPAND_ARGS[] =
 
 static const FnCallArg STRING_MUSTACHE_ARGS[] =
 {
+    {CF_ANYSTRING, CF_DATA_TYPE_STRING, "Mustache template string"},
+    {CF_ANYSTRING, CF_DATA_TYPE_STRING, "CFEngine variable identifier or inline JSON, can be blank"},
     {NULL, CF_DATA_TYPE_NONE, NULL}
 };