diff --git a/src/backend/backend.h b/src/backend/backend.h
index 574cba2..90c8d65 100644
--- a/src/backend/backend.h
+++ b/src/backend/backend.h
@@ -98,7 +98,7 @@ struct backend_operations {
 
 	/// Create a shadow image based on the parameters
 	void *(*render_shadow)(backend_t *backend_data, int width, int height,
-	                       const conv *kernel, double r, double g, double b);
+	                       const conv *kernel, double r, double g, double b, double a);
 
 	// ============ Resource management ===========
 
diff --git a/src/backend/backend_common.c b/src/backend/backend_common.c
index 57592d7..1b3ef19 100644
--- a/src/backend/backend_common.c
+++ b/src/backend/backend_common.c
@@ -148,7 +148,7 @@ make_shadow(xcb_connection_t *c, const conv *kernel, double opacity, int width,
 
 	// Fill part 3
 	for (int y = r; y < height + r; y++) {
-		memset(data + sstride * y + r, 255, width);
+		memset(data + sstride * y + r, 255 * opacity, width);
 	}
 
 	// Part 1
@@ -257,13 +257,13 @@ shadow_picture_err:
 }
 
 void *default_backend_render_shadow(backend_t *backend_data, int width, int height,
-                                    const conv *kernel, double r, double g, double b) {
+                                    const conv *kernel, double r, double g, double b, double a) {
 	xcb_pixmap_t shadow_pixel = solid_picture(backend_data->c, backend_data->root,
 	                                          true, 1, r, g, b),
 	             shadow = XCB_NONE;
 	xcb_render_picture_t pict = XCB_NONE;
 
-	build_shadow(backend_data->c, backend_data->root, 1, width, height, kernel,
+	build_shadow(backend_data->c, backend_data->root, a, width, height, kernel,
 	             shadow_pixel, &shadow, &pict);
 
 	auto visual = x_get_visual_for_standard(backend_data->c, XCB_PICT_STANDARD_ARGB_32);
diff --git a/src/backend/backend_common.h b/src/backend/backend_common.h
index 2c4342a..d0e9136 100644
--- a/src/backend/backend_common.h
+++ b/src/backend/backend_common.h
@@ -32,4 +32,4 @@ bool default_is_win_transparent(void *, win *, void *);
 bool default_is_frame_transparent(void *, win *, void *);
 
 void *default_backend_render_shadow(backend_t *backend_data, int width, int height,
-                                    const conv *kernel, double r, double g, double b);
+                                    const conv *kernel, double r, double g, double b, double a);
diff --git a/src/compton.c b/src/compton.c
index 0f99106..871848d 100644
--- a/src/compton.c
+++ b/src/compton.c
@@ -2010,7 +2010,7 @@ redir_start(session_t *ps) {
               ps->backend_data->ops->render_shadow(ps->backend_data, w->widthb,
                                                    w->heightb, ps->gaussian_map,
                                                    ps->o.shadow_red, ps->o.shadow_green,
-                                                   ps->o.shadow_blue);
+                                                   ps->o.shadow_blue, ps->o.shadow_opacity);
           }
         }
       }
diff --git a/src/win.c b/src/win.c
index a9dd82d..4fdf092 100644
--- a/src/win.c
+++ b/src/win.c
@@ -632,7 +632,7 @@ void win_on_win_size_change(session_t *ps, win *w) {
         w->shadow_image = ps->backend_data->ops->render_shadow(ps->backend_data, w->widthb,
                                                                w->heightb, ps->gaussian_map,
                                                                ps->o.shadow_red, ps->o.shadow_green,
-                                                               ps->o.shadow_blue);
+                                                               ps->o.shadow_blue, ps->o.shadow_opacity);
       }
     } else {
       assert(w->state == WSTATE_UNMAPPED);
@@ -1270,7 +1270,7 @@ void win_update_bounding_shape(session_t *ps, win *w) {
         w->shadow_image = ps->backend_data->ops->render_shadow(ps->backend_data, w->widthb,
                                                                w->heightb, ps->gaussian_map,
                                                                ps->o.shadow_red, ps->o.shadow_green,
-                                                               ps->o.shadow_blue);
+                                                               ps->o.shadow_blue, ps->o.shadow_opacity);
       }
     }
   } else {
@@ -1661,7 +1661,7 @@ void map_win(session_t *ps, win *w) {
         ps->backend_data->ops->render_shadow(ps->backend_data, w->widthb,
                                              w->heightb, ps->gaussian_map,
                                              ps->o.shadow_red, ps->o.shadow_green,
-                                             ps->o.shadow_blue);
+                                             ps->o.shadow_blue, ps->o.shadow_opacity);
     }
   }
   log_debug("Window %#010x has opacity %f, opacity target is %f", w->id, w->opacity, w->opacity_tgt);