diff --git a/Include/boolobject.h b/Include/boolobject.h
index 4e5b99f..0259126 100644
--- a/Include/boolobject.h
+++ b/Include/boolobject.h
@@ -24,7 +24,7 @@
 #define Py_True ((PyObject *) &_Py_TrueStruct)
 
 /* Function to return a bool from a C long */
-PyObject *PyBool_FromLong(long);
+extern DL_IMPORT(PyObject *) PyBool_FromLong(long);
 
 #ifdef __cplusplus
 }