diff --git a/src_main/io/pisharedmemory.cpp b/src_main/io/pisharedmemory.cpp
index 84d083a0..f79d488e 100644
--- a/src_main/io/pisharedmemory.cpp
+++ b/src_main/io/pisharedmemory.cpp
@@ -122,9 +122,10 @@ bool PISharedMemory::openDevice() {
 			return false;
 		}
 		PRIVATE->owner = true;
-		ftruncate(fd, dsize);
 		//piCoutObj << "created" << fd;
 	}
+	if (fd >= 0)
+		ftruncate(fd, dsize);
 	PRIVATE->data = mmap(0, dsize, PROT_READ | PROT_WRITE, MAP_SHARED, fd, 0);
 	::close(fd);
 	if (PRIVATE->data == MAP_FAILED) {