1 files changed, 9 insertions, 3 deletions
diff --git a/src/os_unix.c b/src/os_unix.c
index f4e542146..03ac3e46c 100644
--- a/src/os_unix.c
+++ b/src/os_unix.c
@@ -4910,11 +4910,17 @@ static int unixShmLock(
   int flags                  /* What to do with the lock */
 ){
   unixFile *pDbFd = (unixFile*)fd;      /* Connection holding shared memory */
-  unixShm *p = pDbFd->pShm;             /* The shared memory being locked */
-  unixShmNode *pShmNode = p->pShmNode;  /* The underlying file iNode */
+  unixShm *p;                           /* The shared memory being locked */
+  unixShmNode *pShmNode;                /* The underlying file iNode */
   int rc = SQLITE_OK;                   /* Result code */
   u16 mask;                             /* Mask of locks to take or release */
-  int *aLock = pShmNode->aLock;
+  int *aLock;
+
+  p = pDbFd->pShm;
+  if( p==0 ) return SQLITE_IOERR_SHMLOCK;
+  pShmNode = p->pShmNode;
+  if( NEVER(pShmNode==0) ) return SQLITE_IOERR_SHMLOCK;
+  aLock = pShmNode->aLock;
 
   assert( pShmNode==pDbFd->pInode->pShmNode );
   assert( pShmNode->pInode==pDbFd->pInode );