diff --git a/src/command_events.cc b/src/command_events.cc
index 1fb8f6a3..e3420e92 100644
--- a/src/command_events.cc
+++ b/src/command_events.cc
@@ -313,7 +313,7 @@ void
 initialize_command_events() {
   CMD2_ANY("test.thread_locking", std::tr1::bind(&test_thread_locking));
 
-  CMD2_VAR_BOOL    ("check_hash", true); // Rename
+  CMD2_VAR_BOOL    ("pieces.hash.on_completion", true);
 
   CMD2_ANY_STRING  ("on_ratio",        std::tr1::bind(&apply_on_ratio, std::tr1::placeholders::_2));
 
diff --git a/src/core/download_list.cc b/src/core/download_list.cc
index 951e380c..c5c5396a 100644
--- a/src/core/download_list.cc
+++ b/src/core/download_list.cc
@@ -558,7 +558,7 @@ void
 DownloadList::received_finished(Download* download) {
   check_contains(download);
 
-  if (rpc::call_command_value("check_hash"))
+  if (rpc::call_command_value("pieces.hash.on_completion"))
     // Set some 'checking_finished_thingie' variable to make hash_done
     // trigger correctly, also so it can bork on missing data.
     hash_queue(download, Download::variable_hashing_last);
diff --git a/src/main.cc b/src/main.cc
index 6ef5b88b..2b989f02 100644
--- a/src/main.cc
+++ b/src/main.cc
@@ -446,6 +446,8 @@ main(int argc, char** argv) {
       CMD2_REDIRECT        ("get_session_on_completion", "system.session.on_completion");
       CMD2_REDIRECT        ("set_session_on_completion", "system.session.on_completion.set");
 
+      CMD2_REDIRECT        ("check_hash", "pieces.hash.on_completion.set");
+
       //
       // Download:
       //
diff --git a/src/rpc/command.h b/src/rpc/command.h
index 8798c5af..c73b3e3d 100644
--- a/src/rpc/command.h
+++ b/src/rpc/command.h
@@ -131,9 +131,15 @@ public:
   static const unsigned int max_arguments = 10;
 
   struct stack_type {
-    torrent::Object* begin() { return reinterpret_cast<torrent::Object*>(buffer); }
-    torrent::Object* end()   { return reinterpret_cast<torrent::Object*>(buffer) + max_arguments; }
+    torrent::Object*       begin() { return reinterpret_cast<torrent::Object*>(buffer); }
+    torrent::Object*       end()   { return reinterpret_cast<torrent::Object*>(buffer) + max_arguments; }
     
+    const torrent::Object* begin() const { return reinterpret_cast<const torrent::Object*>(buffer); }
+    const torrent::Object* end()   const { return reinterpret_cast<const torrent::Object*>(buffer) + max_arguments; }
+    
+    torrent::Object&       operator [] (unsigned int idx)       { return *(begin() + idx); }
+    const torrent::Object& operator [] (unsigned int idx) const { return *(begin() + idx); }
+
     static stack_type* from_data(char* data) { return reinterpret_cast<stack_type*>(data); }
 
     char buffer[sizeof(torrent::Object) * max_arguments];
@@ -142,16 +148,16 @@ public:
   Command() {}
   virtual ~Command() {}
 
-  static torrent::Object* argument(unsigned int index) { return m_arguments.begin() + index; }
-  static torrent::Object& argument_ref(unsigned int index) { return *(m_arguments.begin() + index); }
+  static torrent::Object* argument(unsigned int index) { return current_stack.begin() + index; }
+  static torrent::Object& argument_ref(unsigned int index) { return *(current_stack.begin() + index); }
 
-  static stack_type m_arguments;
+  static stack_type current_stack;
 
-  static torrent::Object* stack_begin() { return m_arguments.begin(); }
-  static torrent::Object* stack_end()   { return m_arguments.end(); }
+  static torrent::Object* stack_begin() { return current_stack.begin(); }
+  static torrent::Object* stack_end()   { return current_stack.end(); }
 
-  static torrent::Object* push_stack(const torrent::Object::list_type& args, torrent::Object* tmp_stack);
-  static void             pop_stack(torrent::Object* first_stack, torrent::Object* last_stack);
+  static torrent::Object* push_stack(const torrent::Object::list_type& args, stack_type* stack);
+  static void             pop_stack(stack_type* stack, torrent::Object* last_stack);
 
 protected:
   Command(const Command&);
diff --git a/src/rpc/command_impl.h b/src/rpc/command_impl.h
index 61ea77e6..43fbf5e1 100644
--- a/src/rpc/command_impl.h
+++ b/src/rpc/command_impl.h
@@ -77,23 +77,26 @@ get_target_cast<torrent::File*>(target_type target, int type) {
 }
 
 inline torrent::Object*
-Command::push_stack(const torrent::Object::list_type& args, torrent::Object* tmp_stack) {
+Command::push_stack(const torrent::Object::list_type& args, stack_type* stack) {
   unsigned int idx = 0;
 
   for (torrent::Object::list_const_iterator itr = args.begin(), last = args.end();
        itr != last && idx < Command::max_arguments; itr++, idx++) {
-    new (tmp_stack + idx) torrent::Object(*itr);
-    tmp_stack[idx].swap(*Command::argument(idx));
+    new (&(*stack)[idx]) torrent::Object(*itr);
+    (*stack)[idx].swap(*Command::argument(idx));
   }
 
-  return tmp_stack + idx;
+  return stack->begin() + idx;
 }
 
 inline void
-Command::pop_stack(torrent::Object* first_stack, torrent::Object* last_stack) {
-  while (last_stack-- != first_stack) {
-    last_stack->swap(*Command::argument(std::distance(first_stack, last_stack)));
+Command::pop_stack(stack_type* stack, torrent::Object* last_stack) {
+  while (last_stack-- != stack->begin()) {
+    last_stack->swap(*Command::argument(std::distance(stack->begin(), last_stack)));
     last_stack->~Object();
+
+    // To ensure we catch errors:
+    std::memset(last_stack, 0xAA, sizeof(torrent::Object));
   }
 }
 
diff --git a/src/rpc/command_map.cc b/src/rpc/command_map.cc
index 00a4c4a6..22ee7bd1 100644
--- a/src/rpc/command_map.cc
+++ b/src/rpc/command_map.cc
@@ -55,7 +55,7 @@
 
 namespace rpc {
 
-Command::stack_type Command::m_arguments;
+Command::stack_type Command::current_stack;
 
 CommandMap::~CommandMap() {
   std::vector<const char*> keys;
diff --git a/test/rpc/command_test.cc b/test/rpc/command_test.cc
new file mode 100644
index 00000000..fd0a04b9
--- /dev/null
+++ b/test/rpc/command_test.cc
@@ -0,0 +1,83 @@
+#include "config.h"
+
+#import "command_test.h"
+
+CPPUNIT_TEST_SUITE_REGISTRATION(CommandTest);
+
+bool
+command_stack_all_empty() {
+  return std::find_if(rpc::Command::stack_begin(), rpc::Command::stack_end(),
+                      std::mem_fun_ref(&torrent::Object::is_not_empty)) == rpc::Command::stack_end();
+}
+
+void
+CommandTest::test_stack() {
+  torrent::Object::list_type args;
+  rpc::Command::stack_type stack;
+  torrent::Object* last_stack;
+
+  // Test empty stack.
+  CPPUNIT_ASSERT(command_stack_all_empty());
+
+  last_stack = rpc::Command::push_stack(args, &stack);
+  CPPUNIT_ASSERT(command_stack_all_empty());
+
+  rpc::Command::pop_stack(&stack, last_stack);
+  CPPUNIT_ASSERT(command_stack_all_empty());
+
+  // Test stack with one.
+  args.push_back(int64_t(1));
+
+  last_stack = rpc::Command::push_stack(args, &stack);
+  CPPUNIT_ASSERT(!command_stack_all_empty());
+  CPPUNIT_ASSERT(rpc::Command::stack_begin()->as_value() == 1);
+  
+  rpc::Command::pop_stack(&stack, last_stack);
+  CPPUNIT_ASSERT(command_stack_all_empty());
+
+  // Test stack with two
+  args.clear();
+  args.push_back(int64_t(2));
+  args.push_back(int64_t(3));
+
+  last_stack = rpc::Command::push_stack(args, &stack);
+  CPPUNIT_ASSERT(!command_stack_all_empty());
+  CPPUNIT_ASSERT(rpc::Command::current_stack[0].as_value() == 2);
+  CPPUNIT_ASSERT(rpc::Command::current_stack[1].as_value() == 3);
+  
+  rpc::Command::pop_stack(&stack, last_stack);
+  CPPUNIT_ASSERT(command_stack_all_empty());
+}
+
+void
+CommandTest::test_stack_double() {
+  torrent::Object::list_type args;
+  rpc::Command::stack_type stack_first;
+  rpc::Command::stack_type stack_second;
+  torrent::Object* last_stack_first;
+  torrent::Object* last_stack_second;
+
+  // Test double-stacked.
+  args.push_back(int64_t(1));
+  
+  last_stack_first = rpc::Command::push_stack(args, &stack_first);
+  CPPUNIT_ASSERT(!command_stack_all_empty());
+  CPPUNIT_ASSERT(rpc::Command::current_stack[0].as_value() == 1);
+
+  args.clear();
+  args.push_back(int64_t(2));
+  args.push_back(int64_t(3));
+  
+  last_stack_second = rpc::Command::push_stack(args, &stack_second);
+  CPPUNIT_ASSERT(!command_stack_all_empty());
+  
+  CPPUNIT_ASSERT(rpc::Command::current_stack[0].as_value() == 2);
+  CPPUNIT_ASSERT(rpc::Command::current_stack[1].as_value() == 3);
+
+  rpc::Command::pop_stack(&stack_second, last_stack_second);
+  CPPUNIT_ASSERT(!command_stack_all_empty());
+  CPPUNIT_ASSERT(rpc::Command::current_stack[0].as_value() == 1);
+  
+  rpc::Command::pop_stack(&stack_first, last_stack_first);
+  CPPUNIT_ASSERT(command_stack_all_empty());
+}
diff --git a/test/rpc/command_test.h b/test/rpc/command_test.h
new file mode 100644
index 00000000..f9ca6725
--- /dev/null
+++ b/test/rpc/command_test.h
@@ -0,0 +1,19 @@
+#include <cppunit/extensions/HelperMacros.h>
+
+#include "rpc/command.h"
+
+class CommandTest : public CppUnit::TestFixture {
+  CPPUNIT_TEST_SUITE(CommandTest);
+  CPPUNIT_TEST(test_stack);
+  CPPUNIT_TEST(test_stack_double);
+  CPPUNIT_TEST_SUITE_END();
+
+public:
+  void setUp() { }
+  void tearDown() {}
+
+  void test_stack();
+  void test_stack_double();
+
+private:
+};