diff --git a/lib/compress/zstdmt_compress.c b/lib/compress/zstdmt_compress.c
index 8de54d4a6..4e09a2082 100644
--- a/lib/compress/zstdmt_compress.c
+++ b/lib/compress/zstdmt_compress.c
@@ -541,8 +541,12 @@ size_t ZSTDMT_compressStream(ZSTDMT_CCtx* zcs, ZSTD_outBuffer* output, ZSTD_inBu
 
     /* check if there is any data available to flush */
     {   unsigned const jobID = zcs->doneJobID & zcs->jobIDMask;
-        ZSTDMT_jobDescription job = zcs->jobs[jobID];
-        if (job.jobCompleted) {   /* job completed : output can be flushed */
+        unsigned jobCompleted;
+        pthread_mutex_lock(&zcs->jobCompleted_mutex);
+        jobCompleted = zcs->jobs[jobID].jobCompleted;
+        pthread_mutex_unlock(&zcs->jobCompleted_mutex);
+        if (jobCompleted) {
+            ZSTDMT_jobDescription const job = zcs->jobs[jobID];
             size_t const toWrite = MIN(job.cSize - job.dstFlushed, output->size - output->pos);
             DEBUGLOG(1, "flush %u bytes from job %u ", (U32)toWrite, zcs->doneJobID);
             ZSTDMT_releaseCCtx(zcs->cctxPool, job.cctx);
@@ -556,15 +560,13 @@ size_t ZSTDMT_compressStream(ZSTDMT_CCtx* zcs, ZSTD_outBuffer* output, ZSTD_inBu
             }
             memcpy((char*)output->dst + output->pos, (const char*)job.dstBuff.start + job.dstFlushed, toWrite);
             output->pos += toWrite;
-            job.dstFlushed += toWrite;
+            zcs->jobs[jobID].dstFlushed += toWrite;
             DEBUGLOG(1, "remaining : %u bytes ", (U32)(job.cSize - job.dstFlushed));
-            if (job.dstFlushed == job.cSize) {   /* output buffer fully flushed => go to next one */
+            if (zcs->jobs[jobID].dstFlushed == job.cSize) {   /* output buffer fully flushed => go to next one */
                 ZSTDMT_releaseBuffer(zcs->buffPool, job.dstBuff);
                 zcs->jobs[jobID].dstBuff = g_nullBuffer;
                 zcs->jobs[jobID].jobCompleted = 0;
                 zcs->doneJobID++;
-            } else {
-                zcs->jobs[jobID].dstFlushed = job.dstFlushed;   /* save flush level into zcs for later retrieval */
     }   }   }
 
     /* recommended next input size : fill current input buffer */