diff --git a/src/libCom/osi/os/default/osdSock.c b/src/libCom/osi/os/default/osdSock.c
index 71cf4c384..7f9103d09 100644
--- a/src/libCom/osi/os/default/osdSock.c
+++ b/src/libCom/osi/os/default/osdSock.c
@@ -38,6 +38,7 @@
 #define epicsExportSharedSymbols
 #include "osiThread.h"
 #include "epicsEvent.h"
+#include "epicsMutex.h"
 #include "osiSock.h"
 #include "epicsAssert.h"
 #include "errlog.h"