diff --git a/idl/idl_api.ysl2 b/idl/idl_api.ysl2
index 1eb62ab..179818a 100644
--- a/idl/idl_api.ysl2
+++ b/idl/idl_api.ysl2
@@ -100,12 +100,33 @@ def "func:idl_type_get_resolved_type" {
 
 def "func:idl_type_get_type_of_deftype" {
     param "idltype";
+    const "deftype", "//deftype[@name=$idltype]";
+    const "type_or_typekind", "$deftype/as/@type";
+
     choose {
         when "func:idl_type_is_of_typekind_deftype($idltype)"
-            result "//deftype[@name=$idltype]/as/@type";
+            choose {
+                when "func:idl_typekind_is_generic($type_or_typekind)"
+                    result call "type_of_generic_deftype" with "deftype", "$deftype";
+                otherwise
+                    result "$type_or_typekind";
+            }
         otherwise
             error > idl_resolve_deftype - is not a deftype: «$idltype»;
     }
 }
 
+function "type_of_generic_deftype" {
+    param "deftype";
+    const "generic_type", "$deftype/as/@type";
+
+    > «$generic_type»
+    > <
+    for "$deftype/as/generic/*" {
+        const "param_type", "name()";
+        > «$param_type»«func:autocomma()»
+    }
+    > >
+}
+