diff --git a/miext/sync/misyncshm.c b/miext/sync/misyncshm.c
index f48533dd1..e74ded7e9 100644
--- a/miext/sync/misyncshm.c
+++ b/miext/sync/misyncshm.c
@@ -27,8 +27,10 @@
 #include <unistd.h>
 #include <X11/xshmfence.h>
 
+#include "os/busfault.h"
 #include "os/osdep.h"
 
+#include "os.h"
 #include "scrnintstr.h"
 #include "misync_priv.h"
 #include "misyncstr.h"
@@ -41,18 +43,106 @@ static DevPrivateKeyRec syncShmFencePrivateKey;
 typedef struct _SyncShmFencePrivate {
     struct xshmfence    *fence;
     int                 fd;
+#ifdef BUSFAULT
+    struct busfault     *busfault;
+#endif
 } SyncShmFencePrivateRec, *SyncShmFencePrivatePtr;
 
 #define SYNC_FENCE_PRIV(pFence) \
     (SyncShmFencePrivatePtr) dixLookupPrivate(&(pFence)->devPrivates, &syncShmFencePrivateKey)
 
+#ifdef BUSFAULT
+
+#include <setjmp.h>
+
+#define SYNC_SHM_FENCE_ACCESS(pFence, pPriv, call)                      \
+    do {                                                                \
+        if ((pPriv)->fence && (pPriv)->busfault) {                      \
+            sigjmp_buf jmp;                                             \
+            if (sigsetjmp(jmp, 1) == 0) {                               \
+                busfault_set_jmp((pPriv)->busfault, &jmp);              \
+                call;                                                   \
+                busfault_set_jmp((pPriv)->busfault, NULL);              \
+            } else {                                                    \
+                ErrorF("shared memory fence 0x%x truncated by client\n",\
+                       (unsigned int) (pFence)->sync.id);               \
+                miSyncShmFenceDiscard(pFence);                          \
+            }                                                           \
+        } else if ((pPriv)->fence) {                                    \
+            call;                                                       \
+        }                                                               \
+    } while (0)
+
+
+/* Cover the full mmap VMA; xshmfence maps a small object which the
+ * kernel rounds up to a page. */
+static unsigned int pagesize;
+
+static void
+initPageSize(void)
+{
+    if (!pagesize) {
+#ifdef _SC_PAGESIZE
+        pagesize = sysconf(_SC_PAGESIZE);
+#else
+        pagesize = getpagesize();
+#endif
+    }
+}
+
+static void
+miSyncShmFenceDiscard(SyncFence *pFence)
+{
+    SyncShmFencePrivatePtr pPriv = SYNC_FENCE_PRIV(pFence);
+
+    if (pPriv->busfault) {
+        busfault_unregister(pPriv->busfault);
+        pPriv->busfault = NULL;
+    }
+    if (pPriv->fence) {
+        xshmfence_unmap_shm(pPriv->fence);
+        pPriv->fence = NULL;
+        close(pPriv->fd);
+    }
+}
+
+static void
+miSyncShmFenceBusfaultNotify(void *context)
+{
+    SyncFence *pFence = context;
+
+    ErrorF("shared memory fence 0x%x truncated by client\n",
+           (unsigned int) pFence->sync.id);
+    /* Drop the mapping; the fence XID remains and further ops use
+     * the in-server SyncFence state only. */
+    miSyncShmFenceDiscard(pFence);
+}
+
+static void
+miSyncShmFenceRegisterBusfault(SyncFence *pFence)
+{
+    SyncShmFencePrivatePtr pPriv = SYNC_FENCE_PRIV(pFence);
+
+    pPriv->busfault = busfault_register_mmap(pPriv->fence, pagesize,
+                                             miSyncShmFenceBusfaultNotify,
+                                             pFence);
+    if (!pPriv->busfault)
+        ErrorF("shared memory fence 0x%x could not register for truncation detection\n",
+               (unsigned int) pFence->sync.id);
+}
+#endif /* BUSFAULT */
+
 static void
 miSyncShmFenceSetTriggered(SyncFence * pFence)
 {
     SyncShmFencePrivatePtr      pPriv = SYNC_FENCE_PRIV(pFence);
 
+#ifdef BUSFAULT
+    SYNC_SHM_FENCE_ACCESS(pFence, pPriv, xshmfence_trigger(pPriv->fence));
+#else
     if (pPriv->fence)
         xshmfence_trigger(pPriv->fence);
+#endif
     miSyncFenceSetTriggered(pFence);
 }
 
@@ -61,8 +151,12 @@ miSyncShmFenceReset(SyncFence * pFence)
 {
     SyncShmFencePrivatePtr      pPriv = SYNC_FENCE_PRIV(pFence);
 
+#ifdef BUSFAULT
+    SYNC_SHM_FENCE_ACCESS(pFence, pPriv, xshmfence_reset(pPriv->fence));
+#else
     if (pPriv->fence)
         xshmfence_reset(pPriv->fence);
+#endif
     miSyncFenceReset(pFence);
 }
 
@@ -71,6 +165,24 @@ miSyncShmFenceCheckTriggered(SyncFence * pFence)
 {
     SyncShmFencePrivatePtr      pPriv = SYNC_FENCE_PRIV(pFence);
 
+#ifdef BUSFAULT
+    if (pPriv->fence && pPriv->busfault) {
+        sigjmp_buf jmp;
+        if (sigsetjmp(jmp, 1) == 0) {
+            Bool result;
+
+            busfault_set_jmp(pPriv->busfault, &jmp);
+            result = xshmfence_query(pPriv->fence);
+            busfault_set_jmp(pPriv->busfault, NULL);
+            return result;
+        } else {
+            ErrorF("shared memory fence 0x%x truncated by client\n",
+                   (unsigned int) pFence->sync.id);
+            miSyncShmFenceDiscard(pFence);
+            return miSyncFenceCheckTriggered(pFence);
+        }
+    }
+#endif
     if (pPriv->fence)
         return xshmfence_query(pPriv->fence);
     else
@@ -114,9 +226,15 @@ miSyncShmScreenDestroyFence(ScreenPtr pScreen, SyncFence * pFence)
     SyncShmFencePrivatePtr      pPriv = SYNC_FENCE_PRIV(pFence);
 
     if (pPriv->fence) {
+#ifdef BUSFAULT
+        /* Wake waiters if possible; SIGBUS discards via longjmp. */
+        SYNC_SHM_FENCE_ACCESS(pFence, pPriv, xshmfence_trigger(pPriv->fence));
+        miSyncShmFenceDiscard(pFence);
+#else
         xshmfence_trigger(pPriv->fence);
         xshmfence_unmap_shm(pPriv->fence);
         close(pPriv->fd);
+#endif
     }
     miSyncScreenDestroyFence(pScreen, pFence);
 }
@@ -131,6 +249,9 @@ miSyncShmCreateFenceFromFd(ScreenPtr pScreen, SyncFence *pFence, int fd, Bool in
     fd = os_move_fd(fd);
     pPriv->fence = xshmfence_map_shm(fd);
     if (pPriv->fence) {
+#ifdef BUSFAULT
+        miSyncShmFenceRegisterBusfault(pFence);
+#endif
         pPriv->fd = fd;
         return Success;
     }
@@ -154,6 +275,9 @@ miSyncShmGetFenceFd(ScreenPtr pScreen, SyncFence *pFence)
             close (pPriv->fd);
             return -1;
         }
+#ifdef BUSFAULT
+        miSyncShmFenceRegisterBusfault(pFence);
+#endif
     }
     return pPriv->fd;
 }
@@ -177,6 +301,10 @@ Bool miSyncShmScreenInit(ScreenPtr pScreen)
             return FALSE;
     }
 
+#ifdef BUSFAULT
+    initPageSize();
+#endif
+
     funcs = miSyncGetScreenFuncs(pScreen);
 
     funcs->CreateFence = miSyncShmScreenCreateFence;