diff --git a/core/Debugger.cc b/core/Debugger.cc
index 69f1c09af0ef72e75a42d6228c895eae55bbc0d4..50086a2cb77a8bb28da1de6e969222918a568acd 100644
--- a/core/Debugger.cc
+++ b/core/Debugger.cc
@@ -940,6 +940,7 @@ void TTCN3_Debugger::test_execution_started()
     if (function_calls.cfg == CALLS_STORE_ALL) {
       Free(function_calls.buffer.ptr);
       function_calls.buffer.ptr = NULL;
+      function_calls.buffer.size = 0;
     }
     function_calls.buffer.start = 0;
     function_calls.buffer.end = -1;