diff --git a/ChangeLog b/ChangeLog
index 43faeb83f6..7d94f736c6 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,7 @@
+Tue Oct  4 11:44:10 2011  NARUSE, Yui  <naruse@ruby-lang.org>
+
+	* gc.c (rb_gc_set_params): ruby_verbose can be Qnil, so use RTEST.
+
 Tue Oct  4 08:33:41 2011  Eric Hodel  <drbrain@segment7.net>
 
 	* ext/etc/etc.c:  Document Etc, Etc.sysconfdir, Etc.systmpdir.  Patch
diff --git a/gc.c b/gc.c
index 9f9d6b884a..c59c73696b 100644
--- a/gc.c
+++ b/gc.c
@@ -427,7 +427,7 @@ rb_gc_set_params(void)
     malloc_limit_ptr = getenv("RUBY_GC_MALLOC_LIMIT");
     if (malloc_limit_ptr != NULL) {
 	int malloc_limit_i = atoi(malloc_limit_ptr);
-	if (ruby_verbose)
+	if (RTEST(ruby_verbose))
 	    fprintf(stderr, "malloc_limit=%d (%d)\n",
 		    malloc_limit_i, initial_malloc_limit);
 	if (malloc_limit_i > 0) {
@@ -438,7 +438,7 @@ rb_gc_set_params(void)
     heap_min_slots_ptr = getenv("RUBY_HEAP_MIN_SLOTS");
     if (heap_min_slots_ptr != NULL) {
 	int heap_min_slots_i = atoi(heap_min_slots_ptr);
-	if (ruby_verbose)
+	if (RTEST(ruby_verbose))
 	    fprintf(stderr, "heap_min_slots=%d (%d)\n",
 		    heap_min_slots_i, initial_heap_min_slots);
 	if (heap_min_slots_i > 0) {
@@ -450,7 +450,7 @@ rb_gc_set_params(void)
     free_min_ptr = getenv("RUBY_FREE_MIN");
     if (free_min_ptr != NULL) {
 	int free_min_i = atoi(free_min_ptr);
-	if (ruby_verbose)
+	if (RTEST(ruby_verbose))
 	    fprintf(stderr, "free_min=%d (%d)\n", free_min_i, initial_free_min);
 	if (free_min_i > 0) {
 	    initial_free_min = free_min_i;
diff --git a/test/ruby/test_gc.rb b/test/ruby/test_gc.rb
index a0bc7f8b7f..bcc490626d 100644
--- a/test/ruby/test_gc.rb
+++ b/test/ruby/test_gc.rb
@@ -93,6 +93,8 @@ class TestGc < Test::Unit::TestCase
       "RUBY_HEAP_MIN_SLOTS" => "100000"
     }
     assert_in_out_err([env, "-e", "exit"], "", [], [], "[ruby-core:39795]")
+    assert_in_out_err([env, "-W0", "-e", "exit"], "", [], [], "[ruby-core:39795]")
+    assert_in_out_err([env, "-W1", "-e", "exit"], "", [], [], "[ruby-core:39795]")
     assert_in_out_err([env, "-w", "-e", "exit"], "", [], /heap_min_slots=100000/, "[ruby-core:39795]")
   end
 end