diff --git a/sys/kern/uipc_syscalls.c b/sys/kern/uipc_syscalls.c
--- a/sys/kern/uipc_syscalls.c
+++ b/sys/kern/uipc_syscalls.c
@@ -948,7 +948,8 @@
 		AUDIT_ARG_SOCKADDR(td, AT_FDCWD, fromsa);
 #ifdef KTRACE
 	if (ktruio != NULL) {
-		ktruio->uio_resid = len - auio.uio_resid;
+		/* MSG_TRUNC can trigger underflow of uio_resid. */
+		ktruio->uio_resid = MIN(len - auio.uio_resid, len);
 		ktrgenio(s, UIO_READ, ktruio, error);
 	}
 #endif