diff --git a/src/common.h b/src/common.h
index 9c4c727c..7892d645 100644
--- a/src/common.h
+++ b/src/common.h
@@ -272,12 +272,9 @@ typedef struct session {
 
 	// === Expose event related ===
 	/// Pointer to an array of <code>XRectangle</code>-s of exposed region.
-	/// XXX why do we need this array?
+	/// This is a reuse temporary buffer for handling root expose events.
+	/// This is a dynarr.
 	rect_t *expose_rects;
-	/// Number of <code>XRectangle</code>-s in <code>expose_rects</code>.
-	int size_expose;
-	/// Index of the next free slot in <code>expose_rects</code>.
-	int n_expose;
 
 	struct wm *wm;
 
diff --git a/src/event.c b/src/event.c
index af8ee7c0..a4eb7ac1 100644
--- a/src/event.c
+++ b/src/event.c
@@ -22,6 +22,7 @@
 #include "log.h"
 #include "picom.h"
 #include "region.h"
+#include "utils/dynarr.h"
 #include "utils/misc.h"
 #include "wm/defs.h"
 #include "wm/wm.h"
@@ -495,9 +496,9 @@ static inline void ev_circulate_notify(session_t *ps, xcb_circulate_notify_event
 	}
 }
 
-static inline void expose_root(session_t *ps, const rect_t *rects, int nrects) {
+static inline void expose_root(session_t *ps, const rect_t *rects, size_t nrects) {
 	region_t region;
-	pixman_region32_init_rects(&region, rects, nrects);
+	pixman_region32_init_rects(&region, rects, (int)nrects);
 	add_damage(ps, &region);
 	pixman_region32_fini(&region);
 }
@@ -505,27 +506,19 @@ static inline void expose_root(session_t *ps, const rect_t *rects, int nrects) {
 static inline void ev_expose(session_t *ps, xcb_expose_event_t *ev) {
 	if (ev->window == ps->c.screen_info->root ||
 	    (ps->overlay && ev->window == ps->overlay)) {
-		int more = ev->count + 1;
-		if (ps->n_expose == ps->size_expose) {
-			if (ps->expose_rects) {
-				ps->expose_rects =
-				    crealloc(ps->expose_rects, ps->size_expose + more);
-				ps->size_expose += more;
-			} else {
-				ps->expose_rects = ccalloc(more, rect_t);
-				ps->size_expose = more;
-			}
-		}
+		dynarr_reserve(ps->expose_rects, ev->count + 1);
 
-		ps->expose_rects[ps->n_expose].x1 = ev->x;
-		ps->expose_rects[ps->n_expose].y1 = ev->y;
-		ps->expose_rects[ps->n_expose].x2 = ev->x + ev->width;
-		ps->expose_rects[ps->n_expose].y2 = ev->y + ev->height;
-		ps->n_expose++;
+		rect_t new_rect = {
+		    .x1 = ev->x,
+		    .y1 = ev->y,
+		    .x2 = ev->x + ev->width,
+		    .y2 = ev->y + ev->height,
+		};
+		dynarr_push(ps->expose_rects, new_rect);
 
 		if (ev->count == 0) {
-			expose_root(ps, ps->expose_rects, ps->n_expose);
-			ps->n_expose = 0;
+			expose_root(ps, ps->expose_rects, dynarr_len(ps->expose_rects));
+			dynarr_clear_pod(ps->expose_rects);
 		}
 	}
 }
diff --git a/src/picom.c b/src/picom.c
index a66698da..ebd62d37 100644
--- a/src/picom.c
+++ b/src/picom.c
@@ -63,6 +63,7 @@
 #include "renderer/command_builder.h"
 #include "renderer/layout.h"
 #include "renderer/renderer.h"
+#include "utils/dynarr.h"
 #include "utils/file_watch.h"
 #include "utils/kernel.h"
 #include "utils/list.h"
@@ -2020,8 +2021,6 @@ static session_t *session_init(int argc, char **argv, Display *dpy,
 	    .quit = false,
 
 	    .expose_rects = NULL,
-	    .size_expose = 0,
-	    .n_expose = 0,
 
 	    .black_picture = XCB_NONE,
 	    .cshadow_picture = XCB_NONE,
@@ -2521,6 +2520,7 @@ static session_t *session_init(int argc, char **argv, Display *dpy,
 	}
 
 	ps->command_builder = command_builder_new();
+	ps->expose_rects = dynarr_new(rect_t, 0);
 
 	ps->pending_updates = true;
 
@@ -2591,7 +2591,7 @@ static void session_destroy(session_t *ps) {
 	free_paint(ps, &ps->tgt_buffer);
 
 	pixman_region32_fini(&ps->screen_reg);
-	free(ps->expose_rects);
+	dynarr_free_pod(ps->expose_rects);
 
 	x_free_monitor_info(&ps->monitors);