diff --git a/kong/tools/mime_type.lua b/kong/tools/mime_type.lua
index d9f730a401cc..e4772919e603 100644
--- a/kong/tools/mime_type.lua
+++ b/kong/tools/mime_type.lua
@@ -5,6 +5,8 @@ local ipairs = ipairs
 local lower = string.lower
 local sub = string.sub
 local find = string.find
+local type = type
+local error = error
 
 local WILDCARD = "*"
 
@@ -97,8 +99,11 @@ end
 -- @tparam table other Other mime-type
 -- @treturn boolean Returns `true` if this mime-type includes other, `false` otherwise
 local function includes(this, other)
-  if not other then
-    return false
+  if type(this) ~= "table" then
+    error("this must be a table", 2)
+  end
+  if type(other) ~= "table" then
+    error("other must be a table", 2)
   end
 
   local this_type = this.type
diff --git a/spec/01-unit/26-mime-type_spec.lua b/spec/01-unit/26-mime-type_spec.lua
index 90df31ab8765..6b4d3cbb6a29 100644
--- a/spec/01-unit/26-mime-type_spec.lua
+++ b/spec/01-unit/26-mime-type_spec.lua
@@ -1,5 +1,4 @@
-local parse_mime_type = require "kong.tools.mime_type".parse_mime_type
-local includes = require "kong.tools.mime_type".includes
+local mime_type = require "kong.tools.mime_type"
 
 describe("kong.tools.mime_type", function()
   describe("parse_mime_type()", function()
@@ -72,7 +71,7 @@ describe("kong.tools.mime_type", function()
         }
       }
       for i, case in ipairs(cases) do
-        local type, subtype, params = parse_mime_type(case.mime_type)
+        local type, subtype, params = mime_type.parse_mime_type(case.mime_type)
         local result = { type = type, subtype = subtype, params = params }
         assert.same(case.result, result, "case: " .. i .. " failed" )
       end
@@ -155,9 +154,14 @@ describe("kong.tools.mime_type", function()
       }
 
       for i, case in ipairs(cases) do
-        assert.is_true(includes(case.this, case.other) == case.result, "case: " .. i .. " failed" )
+        assert.is_true(mime_type.includes(case.this, case.other) == case.result, "case: " .. i .. " failed" )
       end
     end)
+
+    it("throws an error for invalid arguments", function()
+      assert.has_error(function() mime_type.includes(nil, {})  end, "this must be a table")
+      assert.has_error(function() mime_type.includes({}, nil)  end, "other must be a table")
+    end)
   end)
 
 end)