diff --git a/mt-gcbench.c b/mt-gcbench.c
index 1ab50a4e0..f72dac66e 100644
--- a/mt-gcbench.c
+++ b/mt-gcbench.c
@@ -330,14 +330,13 @@ int main(int argc, char *argv[]) {
     tree_size(long_lived_tree_depth) * sizeof(Node) +
     tree_size(max_tree_depth) * sizeof(Node) +
     sizeof(DoubleArray) + sizeof(double) * array_size;
-  if (argc != 4) {
-    fprintf(stderr, "usage: %s MULTIPLIER NTHREADS PARALLELISM\n", argv[0]);
+  if (argc < 3 || argc > 4) {
+    fprintf(stderr, "usage: %s MULTIPLIER NTHREADS [GC-OPTIONS]\n", argv[0]);
     return 1;
   }
 
   double multiplier = atof(argv[1]);
   size_t nthreads = atol(argv[2]);
-  size_t parallelism = atol(argv[3]);
 
   if (!(0.1 < multiplier && multiplier < 100)) {
     fprintf(stderr, "Failed to parse heap multiplier '%s'\n", argv[1]);
@@ -348,18 +347,18 @@ int main(int argc, char *argv[]) {
             (int)MAX_THREAD_COUNT, 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 heap_size = heap_max_live * multiplier * nthreads;
 
   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;