diff --git a/bin/compton-trans b/bin/compton-trans
index 612c35de2e..db41cf181f 100755
--- a/bin/compton-trans
+++ b/bin/compton-trans
@@ -114,7 +114,7 @@ fi
 if test x"$action" = x'reset'; then
   xwininfo -root -tree \
   | sed -n 's/^     \(0x[[:xdigit:]]*\).*/\1/p' \
-  | while IFS=$'\n' read wid; do
+  | while IFS=$(printf '\n') read wid; do
     xprop -id "$wid" -remove _NET_WM_WINDOW_OPACITY
   done
   exit 0
diff --git a/src/compton.c b/src/compton.c
index 92935a3dba..8b4d7be1ed 100644
--- a/src/compton.c
+++ b/src/compton.c
@@ -2277,6 +2277,8 @@ static void
 unmap_win(session_t *ps, win *w) {
   if (!w || IsUnmapped == w->a.map_state) return;
 
+  if (w->destroyed) return;
+
   // One last synchronization
   if (w->paint.pixmap)
     xr_sync(ps, w->paint.pixmap, &w->fence);
@@ -3204,17 +3206,18 @@ circulate_win(session_t *ps, XCirculateEvent *ce) {
 }
 
 static void
-finish_destroy_win(session_t *ps, Window id) {
-  win **prev = NULL, *w = NULL;
+finish_destroy_win(session_t *ps, win *w) {
+  assert(w->destroyed);
+  win **prev = NULL, *i = NULL;
 
 #ifdef DEBUG_EVENTS
-  printf_dbgf("(%#010lx): Starting...\n", id);
+  printf_dbgf("(%#010lx): Starting...\n", w->id);
 #endif
 
-  for (prev = &ps->list; (w = *prev); prev = &w->next) {
-    if (w->id == id && w->destroyed) {
+  for (prev = &ps->list; (i = *prev); prev = &i->next) {
+    if (w == i) {
 #ifdef DEBUG_EVENTS
-      printf_dbgf("(%#010lx \"%s\"): %p\n", id, w->name, w);
+      printf_dbgf("(%#010lx \"%s\"): %p\n", w->id, w->name, w);
 #endif
 
       finish_unmap_win(ps, w);
@@ -3240,7 +3243,7 @@ finish_destroy_win(session_t *ps, Window id) {
 
 static void
 destroy_callback(session_t *ps, win *w) {
-  finish_destroy_win(ps, w->id);
+  finish_destroy_win(ps, w);
 }
 
 static void
@@ -3320,7 +3323,8 @@ xerror(Display __attribute__((unused)) *dpy, XErrorEvent *ev) {
 
   if (ev->request_code == ps->composite_opcode
       && ev->minor_code == X_CompositeRedirectSubwindows) {
-    fprintf(stderr, "Another composite manager is already running\n");
+    fprintf(stderr, "Another composite manager is already running "
+        "(and does not handle _NET_WM_CM_Sn correctly)\n");
     exit(1);
   }
 
@@ -4348,6 +4352,16 @@ ev_screen_change_notify(session_t *ps,
   }
 }
 
+inline static void
+ev_selection_clear(session_t *ps,
+    XSelectionClearEvent __attribute__((unused)) *ev) {
+  // The only selection we own is the _NET_WM_CM_Sn selection.
+  // If we lose that one, we should exit.
+  fprintf(stderr, "Another composite manager started and "
+      "took the _NET_WM_CM_Sn selection.\n");
+  exit(1);
+}
+
 #if defined(DEBUG_EVENTS) || defined(DEBUG_RESTACK)
 /**
  * Get a window's name from window ID.
@@ -4440,6 +4454,9 @@ ev_handle(session_t *ps, XEvent *ev) {
     case PropertyNotify:
       ev_property_notify(ps, (XPropertyEvent *)ev);
       break;
+    case SelectionClear:
+      ev_selection_clear(ps, (XSelectionClearEvent *)ev);
+      break;
     default:
       if (ps->shape_exists && ev->type == ps->shape_event) {
         ev_shape_notify(ps, (XShapeEvent *) ev);
@@ -4892,6 +4909,7 @@ register_cm(session_t *ps) {
   if (!ps->o.no_x_selection) {
     unsigned len = strlen(REGISTER_PROP) + 2;
     int s = ps->scr;
+    Atom atom;
 
     while (s >= 10) {
       ++len;
@@ -4901,7 +4919,13 @@ register_cm(session_t *ps) {
     char *buf = malloc(len);
     snprintf(buf, len, REGISTER_PROP "%d", ps->scr);
     buf[len - 1] = '\0';
-    XSetSelectionOwner(ps->dpy, get_atom(ps, buf), ps->reg_win, 0);
+    atom = get_atom(ps, buf);
+
+    if (XGetSelectionOwner(ps->dpy, atom) != None) {
+      fprintf(stderr, "Another composite manager is already running\n");
+      return false;
+    }
+    XSetSelectionOwner(ps->dpy, atom, ps->reg_win, 0);
     free(buf);
   }
 
diff --git a/src/compton.h b/src/compton.h
index 0e27a759f8..24ef2d5aeb 100644
--- a/src/compton.h
+++ b/src/compton.h
@@ -919,7 +919,7 @@ static void
 circulate_win(session_t *ps, XCirculateEvent *ce);
 
 static void
-finish_destroy_win(session_t *ps, Window id);
+finish_destroy_win(session_t *ps, win *w);
 
 static void
 destroy_callback(session_t *ps, win *w);