diff --git a/modules/libcom/src/osi/epicsThread.h b/modules/libcom/src/osi/epicsThread.h
index 82fa04b5b..da16a0b25 100644
--- a/modules/libcom/src/osi/epicsThread.h
+++ b/modules/libcom/src/osi/epicsThread.h
@@ -124,7 +124,10 @@ epicsShareFunc epicsThreadId epicsShareAPI epicsThreadCreate (
 epicsShareFunc epicsThreadId epicsShareAPI epicsThreadMustCreate (
     const char * name, unsigned int priority, unsigned int stackSize,
     EPICSTHREADFUNC funptr,void * parm );
-/** Wait for a joinable thread to exit (return from its main function */
+
+/* This gets undefined in osdThread.h on VxWorks < 6.9 */
+#define EPICS_THREAD_CAN_JOIN
+/** Wait for a joinable thread to exit (return from its main function) */
 epicsShareFunc void epicsThreadMustJoin(epicsThreadId id);
 /** Block the current thread until epicsThreadResume(). */
 epicsShareFunc void epicsShareAPI epicsThreadSuspendSelf(void);
diff --git a/modules/libcom/src/osi/os/Linux/osdThread.h b/modules/libcom/src/osi/os/Linux/osdThread.h
index 40a837e9f..bb1fdcb0a 100644
--- a/modules/libcom/src/osi/os/Linux/osdThread.h
+++ b/modules/libcom/src/osi/os/Linux/osdThread.h
@@ -16,9 +16,6 @@
 #include "ellLib.h"
 #include "epicsEvent.h"
 
-/* This target supports joining threads */
-#define EPICS_THREAD_CAN_JOIN (1)
-
 #ifdef __cplusplus
 extern "C" {
 #endif
diff --git a/modules/libcom/src/osi/os/RTEMS/osdThread.h b/modules/libcom/src/osi/os/RTEMS/osdThread.h
index 84d579c0f..4eef8c01f 100644
--- a/modules/libcom/src/osi/os/RTEMS/osdThread.h
+++ b/modules/libcom/src/osi/os/RTEMS/osdThread.h
@@ -3,13 +3,21 @@
 *     National Laboratory.
 * Copyright (c) 2002 The Regents of the University of California, as
 *     Operator of Los Alamos National Laboratory.
-* EPICS BASE Versions 3.13.7
-* and higher are distributed subject to a Software License Agreement found
-* in file LICENSE that is included with this distribution. 
+* EPICS BASE is distributed subject to a Software License Agreement found
+* in file LICENSE that is included with this distribution.
 \*************************************************************************/
 
-/* This target supports joining threads */
-#define EPICS_THREAD_CAN_JOIN (1)
+#ifndef INC_osdThread_H
+#define INC_osdThread_H
+
+#ifdef __cplusplus
+extern "C" {
+#endif
 
 int epicsThreadGetOssPriorityValue(unsigned int osiPriority);
 
+#ifdef __cplusplus
+}
+#endif
+
+#endif /* INC_osdThread_H */
diff --git a/modules/libcom/src/osi/os/WIN32/osdThread.h b/modules/libcom/src/osi/os/WIN32/osdThread.h
index fe60564d1..69bc364f0 100644
--- a/modules/libcom/src/osi/os/WIN32/osdThread.h
+++ b/modules/libcom/src/osi/os/WIN32/osdThread.h
@@ -3,15 +3,11 @@
 *     National Laboratory.
 * Copyright (c) 2002 The Regents of the University of California, as
 *     Operator of Los Alamos National Laboratory.
-* EPICS BASE Versions 3.13.7
-* and higher are distributed subject to a Software License Agreement found
-* in file LICENSE that is included with this distribution. 
+* EPICS BASE is distributed subject to a Software License Agreement found
+* in file LICENSE that is included with this distribution.
 \*************************************************************************/
 
 #ifndef osdThreadh
 #define osdThreadh
 
-/* This target supports joining threads */
-#define EPICS_THREAD_CAN_JOIN (1)
-
 #endif /* osdThreadh */
diff --git a/modules/libcom/src/osi/os/posix/osdThread.h b/modules/libcom/src/osi/os/posix/osdThread.h
index eee0c825d..8fe8f14eb 100644
--- a/modules/libcom/src/osi/os/posix/osdThread.h
+++ b/modules/libcom/src/osi/os/posix/osdThread.h
@@ -3,9 +3,8 @@
 *     National Laboratory.
 * Copyright (c) 2002 The Regents of the University of California, as
 *     Operator of Los Alamos National Laboratory.
-* EPICS BASE Versions 3.13.7
-* and higher are distributed subject to a Software License Agreement found
-* in file LICENSE that is included with this distribution. 
+* EPICS BASE is distributed subject to a Software License Agreement found
+* in file LICENSE that is included with this distribution.
 \*************************************************************************/
 #ifndef osdThreadh
 #define osdThreadh
@@ -16,9 +15,6 @@
 #include "ellLib.h"
 #include "epicsEvent.h"
 
-/* This target supports joining threads */
-#define EPICS_THREAD_CAN_JOIN (1)
-
 #ifdef __cplusplus
 extern "C" {
 #endif
diff --git a/modules/libcom/src/osi/os/vxWorks/osdThread.c b/modules/libcom/src/osi/os/vxWorks/osdThread.c
index d5b859ade..0ed31389f 100644
--- a/modules/libcom/src/osi/os/vxWorks/osdThread.c
+++ b/modules/libcom/src/osi/os/vxWorks/osdThread.c
@@ -34,7 +34,7 @@
 #include "vxLib.h"
 #include "epicsExit.h"
 
-#if EPICS_THREAD_CAN_JOIN
+#ifdef EPICS_THREAD_CAN_JOIN
   /* The implementation of epicsThreadMustJoin() here uses 2 features
    * of VxWorks that were first introduced in VxWorks 6.9: taskWait(),
    * and the taskSpareFieldGet/Set routines in taskUtilLib.
@@ -188,7 +188,7 @@ void epicsThreadOnce(epicsThreadOnceId *id, void (*func)(void *), void *arg)
     semGive(epicsThreadOnceMutex);
 }
 
-#if EPICS_THREAD_CAN_JOIN
+#ifdef EPICS_THREAD_CAN_JOIN
 
 /* This routine is not static so it appears in the back-trace
  * of a thread that is waiting to be joined.
@@ -286,8 +286,8 @@ epicsThreadId epicsThreadCreateOpt(const char * name,
 
 void epicsThreadMustJoin(epicsThreadId id)
 {
+#ifdef EPICS_THREAD_CAN_JOIN
     const char *fn = "epicsThreadMustJoin";
-#if EPICS_THREAD_CAN_JOIN
     int tid = (int) id;
     SEM_ID joinSem;
     STATUS status;
@@ -340,8 +340,6 @@ void epicsThreadMustJoin(epicsThreadId id)
         }
         cantProceed(fn);
     }
-#else
-    cantProceed("%s called when EPICS_THREAD_CAN_JOIN is 0\n", fn);
 #endif
 }
 
diff --git a/modules/libcom/src/osi/os/vxWorks/osdThread.h b/modules/libcom/src/osi/os/vxWorks/osdThread.h
index 8fa454ce3..15145663b 100644
--- a/modules/libcom/src/osi/os/vxWorks/osdThread.h
+++ b/modules/libcom/src/osi/os/vxWorks/osdThread.h
@@ -3,20 +3,17 @@
 *     National Laboratory.
 * Copyright (c) 2002 The Regents of the University of California, as
 *     Operator of Los Alamos National Laboratory.
-* EPICS BASE Versions 3.13.7
-* and higher are distributed subject to a Software License Agreement found
-* in file LICENSE that is included with this distribution. 
+* EPICS BASE is distributed subject to a Software License Agreement found
+* in file LICENSE that is included with this distribution.
 \*************************************************************************/
+
 #ifndef osdThreadh
 #define osdThreadh
 
 /* VxWorks 6.9 and later can support joining threads */
 
-#if (_WRS_VXWORKS_MAJOR > 6) || \
-    (_WRS_VXWORKS_MAJOR == 6 && _WRS_VXWORKS_MINOR >= 9)
-#   define EPICS_THREAD_CAN_JOIN (1)
-#else
-#   define EPICS_THREAD_CAN_JOIN (0)
+#if (_WRS_VXWORKS_MAJOR == 6 && _WRS_VXWORKS_MINOR < 9)
+#undef EPICS_THREAD_CAN_JOIN
 #endif
 
 #endif /* osdThreadh */