diff --git a/src/libCom/error/Makefile b/src/libCom/error/Makefile
index ce9ca659a..bf81074e8 100644
--- a/src/libCom/error/Makefile
+++ b/src/libCom/error/Makefile
@@ -24,6 +24,7 @@ Com_SRCS += errSymTbl.c
 ERR_S_FILES += $(LIBCOM)/osi/devLib.h
 ERR_S_FILES += $(LIBCOM)/as/asLib.h
 ERR_S_FILES += $(LIBCOM)/misc/epicsStdlib.h
+ERR_S_FILES += $(LIBCOM)/pool/epicsThreadPool.h
 ERR_S_FILES += $(SRC)/ioc/db/dbAccessDefs.h
 ERR_S_FILES += $(SRC)/ioc/dbStatic/devSup.h
 ERR_S_FILES += $(SRC)/ioc/dbStatic/drvSup.h
diff --git a/src/libCom/error/errMdef.h b/src/libCom/error/errMdef.h
index 80483bca1..27b693d8c 100644
--- a/src/libCom/error/errMdef.h
+++ b/src/libCom/error/errMdef.h
@@ -49,6 +49,7 @@ extern "C" {
 #define M_bucket	(525 <<16) /*Bucket Hash*/
 #define M_gddFuncTbl	(526 <<16) /*gdd jump table*/
 #define M_stdlib        (527 <<16) /*EPICS Standard library*/
+#define M_pool          (528 <<16) /*Thread pool*/
 
 epicsShareFunc void epicsShareAPI errSymLookup(long status, char *pBuf, unsigned bufLength);
 epicsShareFunc void epicsShareAPI errSymTest(unsigned short modnum, unsigned short begErrNum, unsigned short endErrNum);
diff --git a/src/libCom/pool/epicsThreadPool.h b/src/libCom/pool/epicsThreadPool.h
index e6b3f03c8..3416bb23a 100644
--- a/src/libCom/pool/epicsThreadPool.h
+++ b/src/libCom/pool/epicsThreadPool.h
@@ -14,6 +14,14 @@
 #include <stdio.h>
 
 #include "shareLib.h"
+#include "errMdef.h"
+
+#define S_pool_jobBusy   (M_pool| 1) /*Job already queued or running*/
+#define S_pool_jobIdle   (M_pool| 2) /*Job was not queued or running*/
+#define S_pool_noPool    (M_pool| 3) /*Job not associated with a pool*/
+#define S_pool_paused    (M_pool| 4) /*Pool not currently accepting jobs*/
+#define S_pool_noThreads (M_pool| 5) /*Can't create worker thread*/
+#define S_pool_timeout   (M_pool| 6) /*Pool still busy after timeout*/
 
 #ifdef __cplusplus
 extern "C" {
diff --git a/src/libCom/pool/poolJob.c b/src/libCom/pool/poolJob.c
index 05645fea0..8e86fb768 100644
--- a/src/libCom/pool/poolJob.c
+++ b/src/libCom/pool/poolJob.c
@@ -125,7 +125,7 @@ int createPoolThread(epicsThreadPool *pool)
                             &workerMain,
                             pool);
     if (!tid)
-        return 1;
+        return S_pool_noThreads;
 
     pool->threadsRunning++;
     pool->threadsSleeping++;
@@ -190,7 +190,7 @@ int epicsJobMove(epicsJob *job, epicsThreadPool *newpool)
 
         if (job->queued || job->running) {
             epicsMutexUnlock(pool->guard);
-            return EINVAL;
+            return S_pool_jobBusy;
         }
 
         ellDelete(&pool->owned, &job->jobnode);
@@ -218,18 +218,18 @@ int epicsJobQueue(epicsJob *job)
     epicsThreadPool *pool = job->pool;
 
     if (!pool)
-        return EINVAL;
+        return S_pool_noPool;
 
     epicsMutexMustLock(pool->guard);
 
     assert(!job->dead);
 
     if (pool->pauseadd) {
-        ret = EPERM;
+        ret = S_pool_paused;
         goto done;
     }
     else if (job->freewhendone) {
-        ret = EINVAL;
+        ret = S_pool_jobBusy;
         goto done;
     }
     else if (job->queued) {
@@ -279,7 +279,7 @@ int epicsJobQueue(epicsJob *job)
                 /* oops, we couldn't lazy create our first worker
                  * so this job would never run!
                  */
-                ret = EAGAIN;
+                ret = S_pool_noThreads;
                 job->queued = 0;
                 /* if threadsRunning==0 then no jobs can be running */
                 assert(!job->running);
@@ -301,11 +301,11 @@ done:
 
 int epicsJobUnqueue(epicsJob *job)
 {
-    int ret = 1;
+    int ret = S_pool_jobIdle;
     epicsThreadPool *pool = job->pool;
 
     if (!pool)
-        return EINVAL;
+        return S_pool_noPool;
 
     epicsMutexMustLock(pool->guard);
 
diff --git a/src/libCom/pool/threadPool.c b/src/libCom/pool/threadPool.c
index 317f4786a..3cfd06606 100644
--- a/src/libCom/pool/threadPool.c
+++ b/src/libCom/pool/threadPool.c
@@ -102,7 +102,7 @@ cleanup:
         epicsMutexDestroy(pool->guard);
 
     free(pool);
-    return 0;
+    return NULL;
 }
 
 static
@@ -175,7 +175,7 @@ int epicsThreadPoolWait(epicsThreadPool *pool, double timeout)
                 cantProceed("epicsThreadPoolWait: failed to wait for Event");
                 break;
             case epicsEventWaitTimeout:
-                ret = ETIMEDOUT;
+                ret = S_pool_timeout;
                 break;
             case epicsEventWaitOK:
                 ret = 0;
diff --git a/src/libCom/test/epicsThreadPoolTest.c b/src/libCom/test/epicsThreadPoolTest.c
index f94b9eb5e..6a4f3f435 100644
--- a/src/libCom/test/epicsThreadPoolTest.c
+++ b/src/libCom/test/epicsThreadPoolTest.c
@@ -191,7 +191,7 @@ static void cleanupjob2(void* arg, epicsJobMode mode)
     if(mode==epicsJobModeCleanup)
         epicsJobDestroy(job); /* delete when threadpool is destroyed */
     else if(mode==epicsJobModeRun)
-        testOk1(epicsJobUnqueue(job)==1);
+        testOk1(epicsJobUnqueue(job)==S_pool_jobIdle);
 }
 static epicsJobFunction cleanupjobs[3] = {&cleanupjob0,&cleanupjob1,&cleanupjob2};
 
@@ -341,23 +341,23 @@ void testcancel(void)
     /* freeze */
     epicsThreadPoolControl(pool, epicsThreadPoolQueueRun, 0);
 
-    testOk1(epicsJobUnqueue(job[0])==1); /* not queued yet */
+    testOk1(epicsJobUnqueue(job[0])==S_pool_jobIdle); /* not queued yet */
 
     epicsJobQueue(job[0]);
     testOk1(epicsJobUnqueue(job[0])==0);
-    testOk1(epicsJobUnqueue(job[0])==1);
+    testOk1(epicsJobUnqueue(job[0])==S_pool_jobIdle);
 
     epicsThreadSleep(0.01);
     epicsJobQueue(job[0]);
     testOk1(epicsJobUnqueue(job[0])==0);
-    testOk1(epicsJobUnqueue(job[0])==1);
+    testOk1(epicsJobUnqueue(job[0])==S_pool_jobIdle);
 
     epicsThreadPoolControl(pool, epicsThreadPoolQueueRun, 1);
 
     epicsJobQueue(job[1]); /* actually let it run this time */
 
     epicsEventMustWait(cancel[0]);
-    testOk1(epicsJobUnqueue(job[0])==1);
+    testOk1(epicsJobUnqueue(job[0])==S_pool_jobIdle);
     epicsEventSignal(cancel[1]);
 
     epicsThreadPoolDestroy(pool);