diff --git a/ets2panda/checker/ets/object.cpp b/ets2panda/checker/ets/object.cpp
index f3c52febcb5f7a8b3148660ee9b89a3bea289fcf..f8b6bee598607956c212b497eff8a9642622bbd4 100644
--- a/ets2panda/checker/ets/object.cpp
+++ b/ets2panda/checker/ets/object.cpp
@@ -444,7 +444,7 @@ Type *ETSChecker::BuildBasicInterfaceProperties(ir::TSInterfaceDeclaration *inte
         type = Program()->IsDeclForDynamicStaticInterop() ? CreateGradualType(interfaceType) : interfaceType;
         var->SetTsType(type);
     } else {
-        interfaceType = var->TsType()->AsETSObjectType();
+        interfaceType = var->TsType()->MaybeBaseTypeOfGradualType()->AsETSObjectType();
         type = Program()->IsDeclForDynamicStaticInterop() ? CreateGradualType(interfaceType) : interfaceType;
     }