diff --git a/src/libponyc/ast/frame.c b/src/libponyc/ast/frame.c
index 817ebe3ba8..662e976c5d 100644
--- a/src/libponyc/ast/frame.c
+++ b/src/libponyc/ast/frame.c
@@ -121,7 +121,7 @@ bool frame_push(typecheck_t* t, ast_t* ast)
       {
         case TK_TYPEPARAM:
         {
-          AST_GET_CHILDREN(parent, id, constraint, def_type);
+          AST_GET_CHILDREN(parent, id, unbounded_type_params, constraint, def_type);
 
           if(constraint == ast)
           {
diff --git a/src/libponyc/ast/lexer.c b/src/libponyc/ast/lexer.c
index 70134fd378..53a6795b72 100644
--- a/src/libponyc/ast/lexer.c
+++ b/src/libponyc/ast/lexer.c
@@ -258,8 +258,11 @@ static const lextoken_t abstract[] =
   { "branch", TK_LITERALBRANCH },
   { "opliteral", TK_OPERATORLITERAL },
 
+  { "_", TK_UNDERSCORE },
   { "typeparams", TK_TYPEPARAMS },
   { "typeparam", TK_TYPEPARAM },
+  { "unboundtypeparams", TK_UNBOUNDTYPEPARAMS },
+  { "unboundtypeparam", TK_UNBOUNDTYPEPARAM },
   { "valueformalparam", TK_VALUEFORMALPARAM },
   { "params", TK_PARAMS },
   { "param", TK_PARAM },
diff --git a/src/libponyc/ast/parser.c b/src/libponyc/ast/parser.c
index d5e6027d25..3f58f6b33a 100644
--- a/src/libponyc/ast/parser.c
+++ b/src/libponyc/ast/parser.c
@@ -122,10 +122,28 @@ DEF(typearg);
   RULE("type argument", type, typeargliteral, typeargconst);
   DONE();
 
-// ID [COLON type] [ASSIGN typearg]
+// UNDERSCORE
+DEF(underscore);
+    AST_NODE(TK_UNBOUNDTYPEPARAM);
+    TOKEN("_", TK_ID);
+    IF(TK_COLON, RULE("type constraint", type));
+    IF(TK_ASSIGN, RULE("default type argument", typearg));
+    DONE();
+
+// LSQUARE UNDERSCORE {COMMA UNDERSCORE} RSQUARE
+DEF(unboundtypeparams);
+    AST_NODE(TK_UNBOUNDTYPEPARAMS);
+    SKIP(NULL, TK_LSQUARE, TK_LSQUARE_NEW);
+    RULE("underscore", underscore);
+    WHILE(TK_COMMA, RULE("underscore", underscore));
+    TERMINATE("higher kinded type arguments", TK_RSQUARE);
+    DONE();
+
+// ID [UNDERSCORE {COMMA UNDERSCORE}] [COLON type] [ASSIGN typearg]
 DEF(typeparam);
   AST_NODE(TK_TYPEPARAM);
   TOKEN("name", TK_ID);
+  OPT RULE("higher kinded type parameters", unboundtypeparams);
   IF(TK_COLON, RULE("type constraint", type));
   IF(TK_ASSIGN, RULE("default type argument", typearg));
   DONE();
diff --git a/src/libponyc/ast/token.c b/src/libponyc/ast/token.c
index a838532bdf..75683033dd 100644
--- a/src/libponyc/ast/token.c
+++ b/src/libponyc/ast/token.c
@@ -177,6 +177,9 @@ const char* token_print(token_t* token)
       return token->printed;
     }
 
+    case TK_UNDERSCORE:
+      return "_";
+
     case TK_LEX_ERROR:
       return "LEX_ERROR";
 
diff --git a/src/libponyc/ast/token.h b/src/libponyc/ast/token.h
index 8592a18af2..502cefd4c3 100644
--- a/src/libponyc/ast/token.h
+++ b/src/libponyc/ast/token.h
@@ -39,6 +39,7 @@ typedef enum token_id
   TK_LSQUARE,
   TK_RSQUARE,
   TK_BACKSLASH,
+  TK_UNDERSCORE,
 
   TK_COMMA,
   TK_ARROW,
@@ -240,6 +241,8 @@ typedef enum token_id
   TK_PACKAGEREF,
   TK_TYPEREF,
   TK_TYPEPARAMREF,
+  TK_UNBOUNDTYPEPARAM,
+  TK_UNBOUNDTYPEPARAMS,
   TK_NEWREF,
   TK_NEWBEREF,
   TK_BEREF,
diff --git a/src/libponyc/ast/treecheckdef.h b/src/libponyc/ast/treecheckdef.h
index d4125d75f0..8bb70cf050 100644
--- a/src/libponyc/ast/treecheckdef.h
+++ b/src/libponyc/ast/treecheckdef.h
@@ -85,9 +85,20 @@ RULE(method,
 
 RULE(type_params, ONE_OR_MORE(type_param), TK_TYPEPARAMS);
 
+RULE(unboundtypeparam,
+  CHILD(id)
+  CHILD(type, none)   // Constraint
+  CHILD(type, none),  // Default
+  TK_UNBOUNDTYPEPARAM);
+
+RULE(unboundtypeparams,
+  ONE_OR_MORE(unboundtypeparam),
+  TK_UNBOUNDTYPEPARAMS);
+
 RULE(type_param,
   HAS_DATA // Original typeparam definition
   CHILD(id)
+  CHILD(unboundtypeparams, none)
   CHILD(type, none)   // Constraint
   CHILD(type, none),  // Default
   TK_TYPEPARAM);
diff --git a/src/libponyc/expr/array.c b/src/libponyc/expr/array.c
index e8f30e93e9..e88464cc6c 100644
--- a/src/libponyc/expr/array.c
+++ b/src/libponyc/expr/array.c
@@ -176,7 +176,7 @@ static void find_possible_element_types(pass_opt_t* opt, ast_t* ast,
     {
       ast_t* def = (ast_t*)ast_data(ast);
       pony_assert(ast_id(def) == TK_TYPEPARAM);
-      find_possible_element_types(opt, ast_childidx(def, 1), list);
+      find_possible_element_types(opt, ast_childidx(def, 2), list);
       return;
     }
 
@@ -217,7 +217,7 @@ static void find_possible_iterator_element_types(pass_opt_t* opt, ast_t* ast,
     {
       ast_t* def = (ast_t*)ast_data(ast);
       pony_assert(ast_id(def) == TK_TYPEPARAM);
-      find_possible_iterator_element_types(opt, ast_childidx(def, 1), list);
+      find_possible_iterator_element_types(opt, ast_childidx(def, 2), list);
       return;
     }
 
diff --git a/src/libponyc/expr/literal.c b/src/libponyc/expr/literal.c
index 1f3aec69f0..0de9ecc878 100644
--- a/src/libponyc/expr/literal.c
+++ b/src/libponyc/expr/literal.c
@@ -264,7 +264,7 @@ static int uifset_formal_param(pass_opt_t* opt, ast_t* type_param_ref,
   pony_assert(ast_id(type_param) == TK_TYPEPARAM);
   pony_assert(chain != NULL);
 
-  ast_t* constraint = ast_childidx(type_param, 1);
+  ast_t* constraint = ast_childidx(type_param, 2);
   pony_assert(constraint != NULL);
 
   // If the constraint is not a subtype of (Real[A] & Number) then there are no
diff --git a/src/libponyc/pass/names.c b/src/libponyc/pass/names.c
index a91be727fa..a1ac48060c 100644
--- a/src/libponyc/pass/names.c
+++ b/src/libponyc/pass/names.c
@@ -174,13 +174,6 @@ static bool names_typeparam(pass_opt_t* opt, ast_t** astp, ast_t* def)
   AST_GET_CHILDREN(ast, package, id, typeargs, cap, ephemeral);
   pony_assert(ast_id(package) == TK_NONE);
 
-  if(ast_id(typeargs) != TK_NONE)
-  {
-    ast_error(opt->check.errors, typeargs,
-      "can't qualify a type parameter with type arguments");
-    return false;
-  }
-
   if(ast_id(ast) == TK_NOMINAL) {
     ast_t* module = ast_nearest(ast, TK_MODULE);
     if(module && ast_get(module, ast_name(id), 0)) {
diff --git a/src/libponyc/pass/sugar.c b/src/libponyc/pass/sugar.c
index 6633c8cd20..f108ad34e0 100644
--- a/src/libponyc/pass/sugar.c
+++ b/src/libponyc/pass/sugar.c
@@ -304,7 +304,7 @@ static ast_result_t sugar_entity(pass_opt_t* opt, ast_t* ast, bool add_create,
 
 static ast_result_t sugar_typeparam(ast_t* ast)
 {
-  AST_GET_CHILDREN(ast, id, constraint);
+  AST_GET_CHILDREN(ast, id, unbound_type_param, constraint);
 
   if(ast_id(constraint) == TK_NONE)
   {
diff --git a/src/libponyc/type/lookup.c b/src/libponyc/type/lookup.c
index f0b75bda08..b05ee8f9da 100644
--- a/src/libponyc/type/lookup.c
+++ b/src/libponyc/type/lookup.c
@@ -236,7 +236,7 @@ static deferred_reification_t* lookup_typeparam(pass_opt_t* opt, ast_t* from,
   ast_t* orig, ast_t* type, const char* name, bool errors, bool allow_private)
 {
   ast_t* def = (ast_t*)ast_data(type);
-  ast_t* constraint = ast_childidx(def, 1);
+  ast_t* constraint = ast_childidx(def, 2);
   ast_t* constraint_def = (ast_t*)ast_data(constraint);
 
   if(def == constraint_def)
diff --git a/src/libponyc/type/reify.c b/src/libponyc/type/reify.c
index 3b4b532b3e..0446fb2b1a 100644
--- a/src/libponyc/type/reify.c
+++ b/src/libponyc/type/reify.c
@@ -163,7 +163,7 @@ bool reify_defaults(ast_t* typeparams, ast_t* typeargs, bool errors,
 
   while(typeparam != NULL)
   {
-    ast_t* defarg = ast_childidx(typeparam, 2);
+    ast_t* defarg = ast_childidx(typeparam, 3);
 
     if(ast_id(defarg) == TK_NONE)
       break;
@@ -424,7 +424,7 @@ bool check_constraints(ast_t* orig, ast_t* typeparams, ast_t* typeargs,
     }
 
     // Reify the constraint.
-    ast_t* constraint = ast_childidx(typeparam, 1);
+    ast_t* constraint = ast_childidx(typeparam, 2);
     ast_t* r_constraint = reify(constraint, typeparams, typeargs, opt,
       true);
 
diff --git a/src/libponyc/type/sanitise.c b/src/libponyc/type/sanitise.c
index 5ef91fd7f9..c42542b778 100644
--- a/src/libponyc/type/sanitise.c
+++ b/src/libponyc/type/sanitise.c
@@ -9,7 +9,7 @@ static void collect_type_param(ast_t* orig_param, ast_t* params, ast_t* args)
   pony_assert(orig_param != NULL);
 
   // Get original type parameter info
-  AST_GET_CHILDREN(orig_param, id, constraint, deflt);
+  AST_GET_CHILDREN(orig_param, id, unbound_type_params, constraint, deflt);
   const char* name = ast_name(id);
 
   constraint = sanitise_type(constraint);
@@ -21,6 +21,7 @@ static void collect_type_param(ast_t* orig_param, ast_t* params, ast_t* args)
     BUILD(new_param, orig_param,
       NODE(TK_TYPEPARAM,
         ID(name)
+        TREE(unbound_type_params)
         TREE(constraint)
         NONE));
 
diff --git a/src/libponyc/type/subtype.c b/src/libponyc/type/subtype.c
index 2af8bdf4fa..ebc64040aa 100644
--- a/src/libponyc/type/subtype.c
+++ b/src/libponyc/type/subtype.c
@@ -313,8 +313,8 @@ static bool is_reified_fun_sub_fun(ast_t* sub, ast_t* super,
 
   while((sub_typeparam != NULL) && (super_typeparam != NULL))
   {
-    ast_t* sub_constraint = ast_childidx(sub_typeparam, 1);
-    ast_t* super_constraint = ast_childidx(super_typeparam, 1);
+    ast_t* sub_constraint = ast_childidx(sub_typeparam, 2);
+    ast_t* super_constraint = ast_childidx(super_typeparam, 2);
 
     if(!is_x_sub_x(super_constraint, sub_constraint, CHECK_CAP_EQ, errorf,
       opt))
diff --git a/src/libponyc/type/typeparam.c b/src/libponyc/type/typeparam.c
index c0d08f726e..907ed6528f 100644
--- a/src/libponyc/type/typeparam.c
+++ b/src/libponyc/type/typeparam.c
@@ -333,6 +333,10 @@ static token_id cap_from_constraint(ast_t* type)
     case TK_TYPEPARAMREF:
       return cap_from_constraint(typeparam_constraint(type));
 
+    // TODO: fix this!
+    case TK_UNBOUNDTYPEPARAM:
+      return cap_from_constraint(typeparam_constraint(type));
+
     default: {}
   }
 
@@ -503,7 +507,7 @@ ast_t* typeparam_constraint(ast_t* typeparamref)
 {
   pony_assert(ast_id(typeparamref) == TK_TYPEPARAMREF);
   ast_t* def = (ast_t*)ast_data(typeparamref);
-  ast_t* constraint = ast_childidx(def, 1);
+  ast_t* constraint = ast_childidx(def, 2);
   astlist_t* def_list = astlist_push(NULL, def);
 
   while(ast_id(constraint) == TK_TYPEPARAMREF)
@@ -517,7 +521,7 @@ ast_t* typeparam_constraint(ast_t* typeparamref)
     }
 
     def_list = astlist_push(def_list, constraint_def);
-    constraint = ast_childidx(constraint_def, 1);
+    constraint = ast_childidx(constraint_def, 2);
   }
 
   astlist_free(def_list);
diff --git a/test/libponyc/badpony.cc b/test/libponyc/badpony.cc
index 7d966a607e..0e6b8a9ac8 100644
--- a/test/libponyc/badpony.cc
+++ b/test/libponyc/badpony.cc
@@ -69,6 +69,19 @@ TEST_F(BadPonyTest, TypeParamMissingForTypeInProvidesList)
   TEST_ERRORS_1(src, "not enough type arguments");
 }
 
+TEST_F(BadPonyTest, HKTMustBeReturnedReified)
+{
+  const char* src =
+    "trait Foo[F[_]]\n"
+    "  fun f[A](): F // F has not been exhaustively parameterized and thus cannot be reified. Should be F[A]\n"
+
+    "actor Main\n"
+    "new create(env: Env) => None";
+
+
+  TEST_ERRORS_1(src, "not enough type arguments");
+}
+
 TEST_F(BadPonyTest, TupleIndexIsZero)
 {
   // From issue #397
diff --git a/test/libponyc/parse_entity.cc b/test/libponyc/parse_entity.cc
index 8cb4bc84a9..eb389f63a3 100644
--- a/test/libponyc/parse_entity.cc
+++ b/test/libponyc/parse_entity.cc
@@ -40,6 +40,20 @@ TEST_F(ParseEntityTest, ActorMinimal)
 }
 
 
+TEST_F(ParseEntityTest, ActorMinimalGeneric)
+{
+  const char* src = "actor Foo[A]";
+
+  TEST_COMPILE(src);
+}
+
+TEST_F(ParseEntityTest, ActorMinimalHKT)
+{
+  const char* src = "actor Foo[F[_]]";
+
+  TEST_COMPILE(src);
+}
+
 TEST_F(ParseEntityTest, ActorCApi)
 {
   const char* src = "actor @ Foo";
diff --git a/test/libponyc/scope.cc b/test/libponyc/scope.cc
index 546be12213..13193bf83c 100644
--- a/test/libponyc/scope.cc
+++ b/test/libponyc/scope.cc
@@ -166,6 +166,18 @@ TEST_F(ScopeTest, TypeParam)
 }
 
 
+TEST_F(ScopeTest, HigherKindedTypeParamMethod)
+{
+  const char* src = "actor A fun foo[F[_]]() => None";
+
+  TEST_COMPILE(src);
+
+  ast_t* foo = lookup_member("A", "foo");
+  ASSERT_ID(TK_FUN, foo);
+  ASSERT_ID(TK_TYPEPARAM, lookup_in(foo, "F"));
+  ASSERT_EQ(1, ref_count(package, "F"));
+}
+
 TEST_F(ScopeTest, Local)
 {
   const char* src = "actor A fun foo() => var bar: U32 = 3";