Index: sys/kern/kern_sig.c
===================================================================
--- sys/kern/kern_sig.c
+++ sys/kern/kern_sig.c
@@ -65,6 +65,7 @@
 #include <sys/namei.h>
 #include <sys/proc.h>
 #include <sys/procdesc.h>
+#include <sys/ptrace.h>
 #include <sys/posix4.h>
 #include <sys/pioctl.h>
 #include <sys/racct.h>
@@ -1320,6 +1321,14 @@
 				error = 0;
 			}
 		}
+
+		/*
+		 * If PTRACE_SCE or PTRACE_SCX were set after
+		 * userspace entered the syscall, return spurious
+		 * EINTR.
+		 */
+		if ((p->p_ptevents & PTRACE_SYSCALL) != 0)
+			error = EINTR;
 	}
 
 	new_block = saved_mask;
@@ -1532,6 +1541,14 @@
 			has_sig += postsig(sig);
 		}
 		mtx_unlock(&p->p_sigacts->ps_mtx);
+
+		/*
+		 * If PTRACE_SCE or PTRACE_SCX were set after
+		 * userspace entered the syscall, return spurious
+		 * EINTR.
+		 */
+		if ((p->p_ptevents & PTRACE_SYSCALL) != 0)
+			has_sig += 1;
 	}
 	PROC_UNLOCK(p);
 	td->td_errno = EINTR;