diff --git a/spec/declaration/local_spec.lua b/spec/declaration/local_spec.lua
index a141056f3..cd7eb9ee7 100644
--- a/spec/declaration/local_spec.lua
+++ b/spec/declaration/local_spec.lua
@@ -551,4 +551,11 @@ describe("local", function()
       { tag = "redeclaration", msg = "variable shadows previous declaration of 'integer'" },
       { tag = "unused", msg = "unused type integer" },
    }))
+
+   it("does not accept type arguments declared twice", util.check_syntax_error([[
+      local type Foo<T> = record<T>
+      end
+   ]], {
+      { y = 1, msg = "cannot declare type arguments twice in type declaration" },
+   }))
 end)
diff --git a/tl.lua b/tl.lua
index 7721c0c60..a249f7ef8 100644
--- a/tl.lua
+++ b/tl.lua
@@ -4049,6 +4049,7 @@ do
          return fail(ps, i, "expected a type name")
       end
       local typeargs
+      local itypeargs = i
       if ps.tokens[i].tk == "<" then
          i, typeargs = parse_anglebracket_list(ps, i, parse_typearg)
       end
@@ -4090,11 +4091,22 @@ do
 
       local nt = asgn.value.newtype
       if nt.typename == "typedecl" then
+         local def = nt.def
+
          if typeargs then
-            nt.typeargs = typeargs
+            if def.typeargs then
+               if def.typeargs then
+                  fail(ps, itypeargs, "cannot declare type arguments twice in type declaration")
+               else
+                  def.typeargs = typeargs
+               end
+            else
+
+
+               nt.typeargs = typeargs
+            end
          end
 
-         local def = nt.def
          if def.fields or def.typename == "enum" then
             if not def.declname then
                def.declname = asgn.var.tk
diff --git a/tl.tl b/tl.tl
index f23eaf146..680a947b3 100644
--- a/tl.tl
+++ b/tl.tl
@@ -4049,6 +4049,7 @@ parse_type_declaration = function(ps: ParseState, i: integer, node_name: NodeKin
       return fail(ps, i, "expected a type name")
    end
    local typeargs: {TypeArgType}
+   local itypeargs = i
    if ps.tokens[i].tk == "<" then
       i, typeargs = parse_anglebracket_list(ps, i, parse_typearg)
    end
@@ -4090,11 +4091,22 @@ parse_type_declaration = function(ps: ParseState, i: integer, node_name: NodeKin
 
    local nt = asgn.value.newtype
    if nt is TypeDeclType then
+      local def = nt.def
+
       if typeargs then
-         nt.typeargs = typeargs
+         if def is HasTypeArgs then
+            if def.typeargs then
+               fail(ps, itypeargs, "cannot declare type arguments twice in type declaration")
+            else
+               def.typeargs = typeargs
+            end
+         else
+            -- FIXME how to resolve type arguments in unions properly
+            -- fail(ps, itypeargs, def.typename .. " does not accept type arguments")
+            nt.typeargs = typeargs
+         end
       end
 
-      local def = nt.def
       if def is RecordLikeType or def is EnumType then
          if not def.declname then
             def.declname = asgn.var.tk