Fix the name of the header file.
diff --git a/Modules/socketmodule.c b/Modules/socketmodule.c
index fb7b046..54d0c4a 100644
--- a/Modules/socketmodule.c
+++ b/Modules/socketmodule.c
@@ -133,7 +133,7 @@
 
 /* Generic _socket.h definitions and includes */
 #define PySocket_BUILDING_SOCKET
-#include "_socket.h"
+#include "socketmodule.h"
 
 /* Addressing includes */