diff --git a/quads.c b/quads.c
index 5e0449875..11d8e5e1f 100644
--- a/quads.c
+++ b/quads.c
@@ -101,24 +101,18 @@ static size_t tree_size(size_t depth) {
 #define MAX_THREAD_COUNT 256
 
 int main(int argc, char *argv[]) {
-  if (argc != 4) {
-    fprintf(stderr, "usage: %s DEPTH MULTIPLIER PARALLELISM\n", argv[0]);
+  if (argc < 3 || 4 < argc) {
+    fprintf(stderr, "usage: %s DEPTH MULTIPLIER [GC-OPTIONS]\n", argv[0]);
     return 1;
   }
 
   size_t depth = parse_size(argv[1], "depth");
   double multiplier = atof(argv[2]);
-  size_t parallelism = atol(argv[3]);
 
   if (!(1.0 < multiplier && multiplier < 100)) {
     fprintf(stderr, "Failed to parse heap multiplier '%s'\n", argv[2]);
     return 1;
   }
-  if (parallelism < 1 || parallelism > MAX_THREAD_COUNT) {
-    fprintf(stderr, "Expected integer between 1 and %d for parallelism, got '%s'\n",
-            (int)MAX_THREAD_COUNT, argv[3]);
-    return 1;
-  }
 
   size_t nquads = tree_size(depth);
   size_t tree_bytes = nquads * sizeof(Quad);
@@ -131,7 +125,12 @@ int main(int argc, char *argv[]) {
   struct gc_options *options = gc_allocate_options();
   gc_options_set_int(options, GC_OPTION_HEAP_SIZE_POLICY, GC_HEAP_SIZE_FIXED);
   gc_options_set_size(options, GC_OPTION_HEAP_SIZE, heap_size);
-  gc_options_set_int(options, GC_OPTION_PARALLELISM, parallelism);
+  if (argc == 4) {
+    if (!gc_options_parse_and_set_many(options, argv[3])) {
+      fprintf(stderr, "Failed to set GC options: '%s'\n", argv[3]);
+      return 1;
+    }
+  }
 
   struct gc_heap *heap;
   struct gc_mutator *mut;