diff --git a/src/sys/pioctl_nt.c b/src/sys/pioctl_nt.c
index 7dc238d511..3a3f83ea40 100644
--- a/src/sys/pioctl_nt.c
+++ b/src/sys/pioctl_nt.c
@@ -844,6 +844,10 @@ pioctl(char *pathp, long opcode, struct ViceIoctl *blobp, int follow)
 
     MarshallString(&preq, fullPath);
     if (blobp->in_size) {
+        if (blobp->in_size > sizeof(preq.data) - (preq.mp - preq.data)*sizeof(char)) {
+            errno = E2BIG;
+            return -1;
+        }
 	memcpy(preq.mp, blobp->in, blobp->in_size);
 	preq.mp += blobp->in_size;
     }