diff --git a/ChangeLog b/ChangeLog
index c3fac3f09c..d8bd162618 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,9 @@
+Wed Jun 25 22:31:32 2014  Nobuyoshi Nakada  <nobu@ruby-lang.org>
+
+	* hash.c (ruby_setenv): fix memory leak on Windows, free
+	  environment strings block after check for the size.
+	  [ruby-dev:48323] [Bug #9977]
+
 Wed Jun 25 15:44:12 2014  Eric Wong  <e@80x24.org>
 
 	* ccan/container_of/container_of.h (container_off_var):
diff --git a/hash.c b/hash.c
index 3c888349da..d6ac93fbc7 100644
--- a/hash.c
+++ b/hash.c
@@ -2750,9 +2750,12 @@ ruby_setenv(const char *name, const char *value)
     int failed = 0;
     check_envname(name);
     if (value) {
-	const char* p = GetEnvironmentStringsA();
+	char* p = GetEnvironmentStringsA();
+	size_t n;
 	if (!p) goto fail; /* never happen */
-	if (strlen(name) + 2 + strlen(value) + getenvsize(p) >= getenvblocksize()) {
+	n = strlen(name) + 2 + strlen(value) + getenvsize(p);
+	FreeEnvironmentStringsA(p);
+	if (n >= getenvblocksize()) {
 	    goto fail;  /* 2 for '=' & '\0' */
 	}
 	buf = rb_sprintf("%s=%s", name, value);
diff --git a/test/ruby/test_env.rb b/test/ruby/test_env.rb
index 41d1ccf306..ecf0608ec6 100644
--- a/test/ruby/test_env.rb
+++ b/test/ruby/test_env.rb
@@ -1,4 +1,5 @@
 require 'test/unit'
+require_relative 'envutil'
 
 class TestEnv < Test::Unit::TestCase
   IGNORE_CASE = /bccwin|mswin|mingw/ =~ RUBY_PLATFORM
@@ -507,4 +508,13 @@ class TestEnv < Test::Unit::TestCase
       end.call
     end
   end
+
+  def test_memory_leak_aset
+    bug9977 = '[ruby-dev:48323] [Bug #9977]'
+    assert_no_memory_leak([], <<-'end;', "5_000.times {ENV[k] = v}", bug9977)
+      ENV.clear
+      k = 'FOO'
+      v = (ENV[k] = 'bar'*5000 rescue 'bar'*1500)
+    end;
+  end
 end