diff --git a/ChangeLog.txt b/ChangeLog.txt
index b5cf92f736..1e909491c7 100644
--- a/ChangeLog.txt
+++ b/ChangeLog.txt
@@ -10,6 +10,26 @@
      * Change, ! Fix, % Optimization, + Addition, - Removal, ; Comment
  */
 
+2014-03-26 14:10 UTC+0100 Przemyslaw Czerpak (druzus/at/poczta.onet.pl)
+  * src/vm/garbage.c
+    ! added protection for activating GC from thread with unlocked HVM stack
+      when other thread is already executing GC passes. Such situation does
+      not happen in core code and the protections is only just in case.
+
+  * src/vm/hvm.c
+    ! do not release HVM thread STOP signal when GC mark pass is activated.
+      It was very serious bug which could cause memory corruption when
+      thread unlocked HVM stack what allow to start GC mark pass by other
+      thread and then locked HVM and begin to change complex variables
+      still scanned by the GC thread. This problem have existed from the
+      beginning when I committed initial version of Harbour MT support.
+      I do not remember why I added code to remove the STOP signal - probably
+      I was experimenting with some new things working on Harbour MT code
+      and I forgot to deactivate it.
+      NOTE: 3-rd party developers who use GC collectible pointer items
+            must not activate any PRG code execution inside their mark
+            functions.
+
 2014-03-25 00:38 UTC+0100 Przemyslaw Czerpak (druzus/at/poczta.onet.pl)
   * tests/iotcp.prg
     ! fixed typo in macro name - thanks to Itamar for the info
diff --git a/src/vm/garbage.c b/src/vm/garbage.c
index a53985e5be..132b58ffef 100644
--- a/src/vm/garbage.c
+++ b/src/vm/garbage.c
@@ -598,7 +598,7 @@ void hb_gcCollectAll( HB_BOOL fForce )
    {
       PHB_GARBAGE pAlloc, pDelete;
 
-      if( ! s_pCurrBlock )
+      if( ! s_pCurrBlock || s_bCollecting )
       {
          hb_vmResumeThreads();
          return;
diff --git a/src/vm/hvm.c b/src/vm/hvm.c
index 78246bdeaf..217bb8f269 100644
--- a/src/vm/hvm.c
+++ b/src/vm/hvm.c
@@ -533,7 +533,6 @@ HB_BOOL hb_vmSuspendThreads( HB_BOOL fWait )
       {
          if( s_iRunningCount <= 0 )
          {
-            hb_vmThreadRequest &= ~HB_THREQUEST_STOP;
             ++s_iRunningCount;
             return HB_TRUE;
          }