diff --git a/grammar.js b/grammar.js
index bf63804..53b1f5f 100644
--- a/grammar.js
+++ b/grammar.js
@@ -320,6 +320,13 @@ module.exports = grammar({
       $.unit_type,
       $.module_pack,
       $.unit,
+      $.polymorphic_type,
+    ),
+
+    polymorphic_type: $ => seq(
+      choice(repeat1($.type_identifier), $.abstract_type),
+      '.',
+      $._inline_type
     ),
 
     tuple_type: $ => prec.dynamic(-1, seq(
@@ -808,7 +815,7 @@ module.exports = grammar({
         $._pattern,
         $.labeled_parameter,
         $.unit,
-        $.type_parameter,
+        $.abstract_type
       ),
     ),
 
@@ -820,7 +827,7 @@ module.exports = grammar({
       optional(field('default_value', $._labeled_parameter_default_value)),
     ),
 
-    type_parameter: $ => seq(
+    abstract_type: $ => seq(
       'type',
       repeat1($.type_identifier),
     ),
diff --git a/test/corpus/functions.txt b/test/corpus/functions.txt
index d8112d8..e58cfe7 100644
--- a/test/corpus/functions.txt
+++ b/test/corpus/functions.txt
@@ -79,7 +79,7 @@ Type annotations
       body: (number))))
 
 ===================================================
-Type arguments
+Abstract type
 ===================================================
 
 let foo = (type a, x: 'a): a => x
@@ -91,7 +91,7 @@ let foo = (type a, x: 'a): a => x
     (value_identifier)
     (function
       (formal_parameters
-        (parameter (type_parameter (type_identifier)))
+        (parameter (abstract_type (type_identifier)))
         (parameter
           (value_identifier)
           (type_annotation (type_identifier))))
diff --git a/test/corpus/type_declarations.txt b/test/corpus/type_declarations.txt
index 82a3b48..454f2f1 100644
--- a/test/corpus/type_declarations.txt
+++ b/test/corpus/type_declarations.txt
@@ -439,6 +439,46 @@ type test = (. ~attr: string) => unit
               (type_identifier)))))
       (unit_type))))
 
+===========================================
+Polymorphic type
+===========================================
+
+let id: 'a. 'a => 'a = x => x
+
+let add: type a. (number<a>, number<a>) => a
+
+---
+
+(source_file
+  (let_binding
+    (value_identifier)
+    (type_annotation
+      (polymorphic_type
+        (type_identifier)
+        (function_type
+          (function_type_parameters (type_identifier))
+          (type_identifier))))
+    (function
+      (value_identifier)
+      (value_identifier)))
+
+  (let_binding
+    (value_identifier)
+    (type_annotation
+      (polymorphic_type
+        (abstract_type (type_identifier))
+        (function_type
+          (function_type_parameters
+            (parameter
+              (generic_type
+                (type_identifier)
+                (type_arguments (type_identifier))))
+            (parameter
+              (generic_type
+                (type_identifier)
+                (type_arguments
+                  (type_identifier))))) (type_identifier))))))
+
 ===========================================
 Variance annotations
 ===========================================