diff --git a/spec/invalid_property_spec.lua b/spec/invalid_property_spec.lua
new file mode 100644
index 0000000..258e85c
--- /dev/null
+++ b/spec/invalid_property_spec.lua
@@ -0,0 +1,41 @@
+local Parser = require "argparse"
+
+describe("invalid property detection", function()
+   it("detects properties with invalid type", function()
+      assert.has_error(function()
+         Parser():name(12345)
+      end, "bad property 'name' (string expected, got number)")
+
+      assert.has_error(function()
+         Parser():option "--foo":convert(true)
+      end, "bad property 'convert' (function or table expected, got boolean)")
+   end)
+
+   it("detects invalid count and args properties", function()
+      assert.has_error(function()
+         Parser():option "--foo":count(false)
+      end, "bad property 'count' (number or string expected, got boolean)")
+
+      assert.has_error(function()
+         Parser():option "--foo":args({})
+      end, "bad property 'args' (number or string expected, got table)")
+
+      assert.has_error(function()
+         Parser():option "--foo":count("foobar")
+      end, "bad property 'count'")
+
+      assert.has_error(function()
+         Parser():option "--foo":args("123-")
+      end, "bad property 'args'")
+   end)
+
+   it("detects unknown named actions", function()
+      assert.has_error(function()
+         Parser():option "--foo":action(false)
+      end, "bad property 'action' (function or string expected, got boolean)")
+
+      assert.has_error(function()
+         Parser():option "--foo":action("catcat")
+      end, "unknown action 'catcat'")
+   end)
+end)