diff --git a/src/data.h b/src/data.h
index 481a245e..90e0a883 100644
--- a/src/data.h
+++ b/src/data.h
@@ -82,8 +82,12 @@ struct gpgme_data
 #ifdef _POSIX_PIPE_BUF
 #define BUFFER_SIZE _POSIX_PIPE_BUF
 #else
+#ifdef HAVE_W32_SYSTEM
+#define BUFFER_SIZE 4096
+#else
 #define BUFFER_SIZE 512
 #endif
+#endif
 #endif
   char pending[BUFFER_SIZE];
   int pending_len;