diff --git a/sys/kern/kern_sig.c b/sys/kern/kern_sig.c
--- a/sys/kern/kern_sig.c
+++ b/sys/kern/kern_sig.c
@@ -174,7 +174,7 @@
     "Discard ignored signals on delivery, otherwise queue them to "
     "the target queue");
 
-static bool pt_attach_transparent = true;
+bool pt_attach_transparent = true;
 SYSCTL_BOOL(_debug, OID_AUTO, ptrace_attach_transparent, CTLFLAG_RWTUN,
     &pt_attach_transparent, 0,
     "Hide wakes from PT_ATTACH on interruptible sleeps");
diff --git a/sys/kern/sys_process.c b/sys/kern/sys_process.c
--- a/sys/kern/sys_process.c
+++ b/sys/kern/sys_process.c
@@ -39,6 +39,7 @@
 #include <sys/mman.h>
 #include <sys/mutex.h>
 #include <sys/reg.h>
+#include <sys/sleepqueue.h>
 #include <sys/syscallsubr.h>
 #include <sys/sysent.h>
 #include <sys/sysproto.h>
@@ -1233,6 +1234,7 @@
 				    (u_long)(uintfptr_t)addr);
 				if (error)
 					goto out;
+				td2->td_dbgflags |= TDB_USERWR;
 			}
 			switch (req) {
 			case PT_TO_SCE:
@@ -1345,6 +1347,27 @@
 		if (data == SIGKILL)
 			proc_wkilled(p);
 
+		/*
+		 * If the PT_CONTINUE-like operation is attempted on
+		 * the thread on sleepq, this is possible only after
+		 * the transparent PT_ATTACH.  In this case, if the
+		 * caller modified the thread state, e.g. by writing
+		 * register file or specifying the pc, make the thread
+		 * xstopped by waking it up.
+		 */
+		if ((td2->td_dbgflags & TDB_USERWR) != 0) {
+			if (pt_attach_transparent) {
+				thread_lock(td2);
+				if (TD_ON_SLEEPQ(td2) &&
+				    (td2->td_flags & TDF_SINTR) != 0) {
+					sleepq_abort(td2, EINTR);
+				} else {
+					thread_unlock(td2);
+				}
+			}
+			td2->td_dbgflags &= ~TDB_USERWR;
+		}
+
 		/*
 		 * Unsuspend all threads.  To leave a thread
 		 * suspended, use PT_SUSPEND to suspend it before
diff --git a/sys/sys/signalvar.h b/sys/sys/signalvar.h
--- a/sys/sys/signalvar.h
+++ b/sys/sys/signalvar.h
@@ -270,6 +270,7 @@
 
 #ifdef _KERNEL
 extern bool sigfastblock_fetch_always;
+extern bool pt_attach_transparent;
 
 /* Return nonzero if process p has an unmasked pending signal. */
 #define	SIGPENDING(td)							\