diff --git a/src/libCom/osi/osiSock.h b/src/libCom/osi/osiSock.h
index 93070f06a..a75204d8e 100644
--- a/src/libCom/osi/osiSock.h
+++ b/src/libCom/osi/osiSock.h
@@ -174,6 +174,7 @@ epicsShareFunc osiSockAddr epicsShareAPI osiLocalAddr (SOCKET socket);
  * mechanisms.
  */
 epicsShareFunc void epicsShareAPI epicsSocketEnableInterruptedSystemCall ();
+struct epicsThreadOSD;
 epicsShareFunc void epicsShareAPI epicsSocketInterruptSystemCall ( struct epicsThreadOSD * );
 
 #ifdef __cplusplus