diff --git a/msvc/ecl-threads.def b/msvc/ecl-threads.def
index 5ea74b410..5051764f1 100755
--- a/msvc/ecl-threads.def
+++ b/msvc/ecl-threads.def
@@ -1316,6 +1316,7 @@ EXPORTS
 	cl_typep
 	cl_coerce
 	cl_subtypep
+	si_do_deftype
 
 	; seq.lsp
 
diff --git a/msvc/ecl.def b/msvc/ecl.def
index dcec4985c..82fcc0ae8 100644
--- a/msvc/ecl.def
+++ b/msvc/ecl.def
@@ -1293,6 +1293,7 @@ EXPORTS
 	cl_typep
 	cl_coerce
 	cl_subtypep
+	si_do_deftype
 
 	; seq.lsp