diff --git a/Include/accu.h b/Include/accu.h
index 9655d37..3636ea6 100644
--- a/Include/accu.h
+++ b/Include/accu.h
@@ -16,6 +16,8 @@
 extern "C" {
 #endif
 
+#undef small /* defined by some Windows headers */
+
 typedef struct {
     PyObject *large;  /* A list of previously accumulated large strings */
     PyObject *small;  /* Pending small strings */