diff --git a/proc/breakpoints.go b/proc/breakpoints.go
index 3acf51f0..ae51d364 100644
--- a/proc/breakpoints.go
+++ b/proc/breakpoints.go
@@ -90,8 +90,15 @@ func (dbp *Process) setBreakpoint(tid int, addr uint64, temp bool) (*Breakpoint,
 		if used {
 			continue
 		}
-		for t, _ := range dbp.Threads {
-			if err := dbp.setHardwareBreakpoint(i, t, addr); err != nil {
+		for tid, t := range dbp.Threads {
+			if t.running {
+				err := t.Halt()
+				if err != nil {
+					return nil, err
+				}
+				defer t.Continue()
+			}
+			if err := dbp.setHardwareBreakpoint(i, tid, addr); err != nil {
 				return nil, fmt.Errorf("could not set hardware breakpoint on thread %d: %s", t, err)
 			}
 		}
diff --git a/proc/proc_linux.go b/proc/proc_linux.go
index 53414d32..90b47225 100644
--- a/proc/proc_linux.go
+++ b/proc/proc_linux.go
@@ -271,12 +271,15 @@ func (dbp *Process) trapWait(pid int) (*Thread, error) {
 			continue
 		}
 		if status.StopSignal() == sys.SIGTRAP {
+			th.running = false
 			return dbp.handleBreakpointOnThread(wpid)
 		}
 		if status.StopSignal() == sys.SIGTRAP && dbp.halt {
+			th.running = false
 			return th, nil
 		}
 		if status.StopSignal() == sys.SIGSTOP && dbp.halt {
+			th.running = false
 			return nil, ManualStopError{}
 		}
 		if th != nil {
diff --git a/proc/threads.go b/proc/threads.go
index 859d6ddb..ed15714e 100644
--- a/proc/threads.go
+++ b/proc/threads.go
@@ -65,7 +65,11 @@ func (thread *Thread) Continue() error {
 // Otherwise we simply execute the next instruction.
 func (thread *Thread) Step() (err error) {
 	thread.singleStepping = true
-	defer func() { thread.singleStepping = false }()
+	thread.running = true
+	defer func() {
+		thread.singleStepping = false
+		thread.running = false
+	}()
 	pc, err := thread.PC()
 	if err != nil {
 		return err
diff --git a/proc/threads_darwin.go b/proc/threads_darwin.go
index 7ef1e154..40a1271a 100644
--- a/proc/threads_darwin.go
+++ b/proc/threads_darwin.go
@@ -18,6 +18,7 @@ func (t *Thread) Halt() error {
 	if kret != C.KERN_SUCCESS {
 		return fmt.Errorf("could not suspend thread %d", t.Id)
 	}
+	t.running = false
 	return nil
 }
 
@@ -35,6 +36,7 @@ func (t *Thread) singleStep() error {
 }
 
 func (t *Thread) resume() error {
+	t.running = true
 	// TODO(dp) set flag for ptrace stops
 	var err error
 	t.dbp.execPtraceFunc(func() { err = PtraceCont(t.dbp.Pid, 0) })
diff --git a/proc/threads_linux.go b/proc/threads_linux.go
index 28572b07..e737463a 100644
--- a/proc/threads_linux.go
+++ b/proc/threads_linux.go
@@ -18,16 +18,18 @@ func (t *Thread) Halt() error {
 	}
 	err := sys.Tgkill(t.dbp.Pid, t.Id, sys.SIGSTOP)
 	if err != nil {
-		return fmt.Errorf("Halt err %s %d", err, t.Id)
+		return fmt.Errorf("halt err %s on thread %d", err, t.Id)
 	}
 	_, _, err = wait(t.Id, 0)
 	if err != nil {
-		return fmt.Errorf("wait err %s %d", err, t.Id)
+		return fmt.Errorf("wait err %s on thread %d", err, t.Id)
 	}
+	t.running = false
 	return nil
 }
 
 func (t *Thread) resume() (err error) {
+	t.running = true
 	t.dbp.execPtraceFunc(func() { err = PtraceCont(t.Id, 0) })
 	return
 }