diff --git a/src/resty/aws/init.lua b/src/resty/aws/init.lua
index 8422a52..92e79fb 100644
--- a/src/resty/aws/init.lua
+++ b/src/resty/aws/init.lua
@@ -303,13 +303,16 @@ local function generate_service_methods(service)
                               method_name)
 
     service[method_name] = function(self, params)
+      params = params or {}
 
       --print(require("pl.pretty").write(self.config))
 
-      -- validate parameters
-      local ok, err = validate_input(params, operation.input, "params")
-      if not ok then
-        return nil, operation_prefix .. " validation error: " .. tostring(err)
+      -- validate parameters if we have any; eg. S3 "listBuckets" has none
+      if operation.input then
+        local ok, err = validate_input(params, operation.input, "params")
+        if not ok then
+          return nil, operation_prefix .. " validation error: " .. tostring(err)
+        end
       end
 
       -- implement stsRegionalEndpoints config setting,
diff --git a/src/resty/aws/request/build.lua b/src/resty/aws/request/build.lua
index 6ed96a2..d2bcef2 100644
--- a/src/resty/aws/request/build.lua
+++ b/src/resty/aws/request/build.lua
@@ -157,7 +157,7 @@ local function build_request(operation, config, params)
 
   -- inject parameters in the right places; path/query/header/body
   -- this assumes they all live on the top-level of the structure, is this correct??
-  for name, member_config in pairs(operation.input.members) do
+  for name, member_config in pairs((operation.input or {}).members or {}) do
     local param_value = params[name]
     -- TODO: date-time value should be properly formatted???
     if param_value ~= nil then