diff --git a/src/mfast/ext_ref.h b/src/mfast/ext_ref.h
index c9a569f..ee75577 100644
--- a/src/mfast/ext_ref.h
+++ b/src/mfast/ext_ref.h
@@ -101,7 +101,7 @@ class ext_cref : public ext_ref_properties<OpType, Properties> {
   explicit ext_cref(const field_cref &base) : base_(base) {}
   explicit ext_cref(const aggregate_cref &base) : base_(base) {}
   cref_type get() const { return base_; }
-  bool present() const { return !this->optional() || base_.present(); }
+  bool present() const { return !static_cast<cref_type*>(this)->optional() || base_.present(); }
 
 private:
   cref_type base_;
@@ -128,7 +128,7 @@ class ext_cref<decimal_cref, std::tuple<ExponentOp, MantissaOp>, Properties> {
   exponent_type get_exponent() const {
     return exponent_type(base_.get_exponent());
   }
-  bool present() const { return !this->optional() || base_.present(); }
+  bool present() const { return !static_cast<cref_type*>(this)->optional() || base_.present(); }
 
 private:
   decimal_cref base_;
@@ -193,7 +193,7 @@ class ext_cref<nested_message_cref, group_type_tag, Properties>
 
   explicit ext_cref(const field_cref &other) : base_(other) {}
   cref_type get() const { return cref_type(aggregate_cref(base_)[0]); }
-  bool present() const { return !this->optional() || base_.present(); }
+  bool present() const { return !static_cast<cref_type*>(this)->optional() || base_.present(); }
 
 private:
   field_cref base_;