Index: generic/tclVar.c
==================================================================
--- generic/tclVar.c
+++ generic/tclVar.c
@@ -1738,10 +1738,11 @@
 				 * any of TCL_GLOBAL_ONLY, TCL_NAMESPACE_ONLY,
 				 * TCL_APPEND_VALUE, TCL_LIST_ELEMENT, or
 				 * TCL_LEAVE_ERR_MSG. */
 {
     Var *varPtr, *arrayPtr;
+    int newValRefCnt = newValuePtr->refCount; /* save original refCount */
 
     /*
      * Filter to pass through only the flags this interface supports.
      */
 
@@ -1748,11 +1749,19 @@
     flags &= (TCL_GLOBAL_ONLY|TCL_NAMESPACE_ONLY|TCL_LEAVE_ERR_MSG
 	    |TCL_APPEND_VALUE|TCL_LIST_ELEMENT);
     varPtr = TclObjLookupVarEx(interp, part1Ptr, part2Ptr, flags, "set",
 	    /*createPart1*/ 1, /*createPart2*/ 1, &arrayPtr);
     if (varPtr == NULL) {
-	if (newValuePtr->refCount == 0) {
+	/* 
+	 * Free newValuePtr only if it had previously no references (otherwise
+	 * the pointer newValRefCnt may be already released (during lookup, 
+	 * by rewriting of interpreter state with error, by trace call, etc.)
+	 *
+	 * TODO: check this can be sane rewritten using something like flag
+	 * TCL_OWN_OBJREF as suggested in ticket [578155d5a19b348d].
+	 */
+	if (newValRefCnt == 0) { /* not set and no other references */
 	    Tcl_DecrRefCount(newValuePtr);
 	}
 	return NULL;
     }
 
@@ -1805,10 +1814,11 @@
 				 * found. */
 {
     Interp *iPtr = (Interp *) interp;
     Tcl_Obj *oldValuePtr;
     Tcl_Obj *resultPtr = NULL;
+    int newValRefCnt = newValuePtr->refCount;  /* save original refCount */
     int result;
 
     /*
      * If the variable is in a hashtable and its hPtr field is NULL, then we
      * may have an upvar to an array element where the array was deleted or an
@@ -1919,11 +1929,11 @@
 		    TclDecrRefCount(oldValuePtr);
 		    oldValuePtr = varPtr->value.objPtr;
 		    Tcl_IncrRefCount(oldValuePtr);	/* Since var is ref */
 		}
 		Tcl_AppendObjToObj(oldValuePtr, newValuePtr);
-		if (newValuePtr->refCount == 0) {
+		if (newValRefCnt == 0) { /* not set and no other references */
 		    Tcl_DecrRefCount(newValuePtr);
 		}
 	    }
 	}
     } else if (newValuePtr != oldValuePtr) {
@@ -1979,11 +1989,11 @@
 	TclCleanupVar(varPtr, arrayPtr);
     }
     return resultPtr;
 
   earlyError:
-    if (newValuePtr->refCount == 0) {
+    if (newValRefCnt == 0) { /* not set and no other references */
 	Tcl_DecrRefCount(newValuePtr);
     }
     goto cleanup;
 }