diff --git a/multibrot.c b/multibrot.c
index a6bb2ca..772c528 100644
--- a/multibrot.c
+++ b/multibrot.c
@@ -38,6 +38,7 @@ void compmandelbrot_line(bitmap_t * mbrot, size_t y) {
 
     bool diverges = false;
     float complex z = 0;
+
     int it;
     for (it = 1; it <= max_it; it++) {
       /* z = z² + c */
@@ -62,6 +63,9 @@ void compmandelbrot_line(bitmap_t * mbrot, size_t y) {
   }
 }
 
+/* Mandelbrot bitmap. */
+bitmap_t *mbrot;
+
 /* Next line to compute. */
 size_t next_y = 0;
 
@@ -70,8 +74,6 @@ pthread_mutex_t next_y_mutex;
 
 /* Thread to compute mandelbrot. */
 void *compmandelbrot(void *arg) {
-  bitmap_t *mbrot = (bitmap_t *) arg;
-
   size_t y = 0;
   while (y < mbrot->height) {
     int ret;
@@ -191,11 +193,11 @@ int main(int argc, char *argv[]) {
   }
 
   /* Set up mandelbrot bitmap. */
-  bitmap_t mbrot;
-  mbrot.width = 1600;
-  mbrot.height = 1200;
-  mbrot.pixels = calloc(sizeof(pixel_t), mbrot.width * mbrot.height);
-  assert(mbrot.pixels != NULL);
+  mbrot = calloc(sizeof(bitmap_t), 1);
+  mbrot->width = 1600;
+  mbrot->height = 1200;
+  mbrot->pixels = calloc(sizeof(pixel_t), mbrot->width * mbrot->height);
+  assert(mbrot->pixels != NULL);
 
   /* Start computing threads. */
   int ret;
@@ -207,7 +209,7 @@ int main(int argc, char *argv[]) {
 
   for (int t = 0; t < num_threads; t++) {
     ret =
-        pthread_create(&threads[t], NULL, compmandelbrot, (void *) &mbrot);
+        pthread_create(&threads[t], NULL, compmandelbrot, (void *) NULL);
     assert(ret == 0);
   }
 
@@ -219,13 +221,14 @@ int main(int argc, char *argv[]) {
 
   /* Save PNG */
   char *file = "multibrot.png";
-  ret = save_png_to_file(&mbrot, file);
+  ret = save_png_to_file(mbrot, file);
   assert(ret == 0);
 
   /* Quit. */
   pthread_exit(NULL);
   free(threads);
-  free(mbrot.pixels);
+  free(mbrot->pixels);
+  free(mbrot);
   ret = pthread_mutex_destroy(&next_y_mutex);
   assert(ret == 0);
   return 0;