diff --git a/common/core/desktop/src/kmx/kmx_xstring.cpp b/common/core/desktop/src/kmx/kmx_xstring.cpp
index 921cca5af7..615f58ef07 100644
--- a/common/core/desktop/src/kmx/kmx_xstring.cpp
+++ b/common/core/desktop/src/kmx/kmx_xstring.cpp
@@ -179,10 +179,9 @@ PKMX_WCHAR km::kbp::kmx::decxstr(PKMX_WCHAR p, PKMX_WCHAR pStart)
   {
     for (int i = 1; i < 5; i++)
     {
-      //   *(p - i) == UC_SENTINEL  &&  next CODE_ right to UC_SENTINEL ( looked up in CODE__SIZE+1) has value i
-      if ((*(p - i) == UC_SENTINEL) && (CODE__SIZE[*(p - i + 1)] + 1 == i)) {
+      //   p right of pstart &&  *(p - i) == UC_SENTINEL  &&  next CODE_ right of UC_SENTINEL ( looked up in CODE__SIZE+1) has value i
+      if ((p >= pStart + i)  && (*(p - i) == UC_SENTINEL) && (CODE__SIZE[*(p - i + 1)] + 1 == i))
         return (p - (CODE__SIZE[*(p - i + 1)] + 1));
-      }
     }
   }
   return p; 
diff --git a/common/core/desktop/tests/unit/kmnkbd/test_kmx_xstring.cpp b/common/core/desktop/tests/unit/kmnkbd/test_kmx_xstring.cpp
index 4f088ac1eb..634f0fe351 100644
--- a/common/core/desktop/tests/unit/kmnkbd/test_kmx_xstring.cpp
+++ b/common/core/desktop/tests/unit/kmnkbd/test_kmx_xstring.cpp
@@ -30,7 +30,102 @@ void test_decxstr() {
     PKMX_WCHAR p_start; // pointer start of input 
     PKMX_WCHAR p;       // pointer end of input
     PKMX_WCHAR q;       // pointer output
-           
+
+
+    // -------------------------------------------------------------------------------------------------------------------------------------------------------
+    // more tests: check if we might end up left of pstart
+    // -------------------------------------------------------------------------------------------------------------------------------------------------------
+
+    p_start = (PKMX_WCHAR)u"\u0001";
+    p       = find_ptr_to_last_character(p_start);
+    q       = decxstr(p, p_start);
+    assert(q == (NULL ));
+
+    p_start = (PKMX_WCHAR)u"\u0001\u0001";
+    p       = find_ptr_to_last_character(p_start);
+    q       = decxstr(p, p_start);
+    assert(q == (p - 1));
+
+    p_start = (PKMX_WCHAR)u"\u0001\u0001\u0001";
+    p       = find_ptr_to_last_character(p_start);
+    q       = decxstr(p, p_start);
+    assert(q == (p - 1));
+
+    p_start = (PKMX_WCHAR)u"\uFFFF\u0001";
+    p       = find_ptr_to_last_character(p_start);
+    q       = decxstr(p, p_start);
+    assert(q == (p - 1));
+
+    p_start = (PKMX_WCHAR)u"\uFFFF\u0001\u0001";
+    p       = find_ptr_to_last_character(p_start);
+    q       = decxstr(p, p_start);
+    assert(q == (p - 2));
+
+    p_start = (PKMX_WCHAR)u"\uFFFF\u0001\u0001\u0001";
+    p       = find_ptr_to_last_character(p_start);
+    q       = decxstr(p, p_start);
+    assert(q == (p - 3));
+
+    p_start = (PKMX_WCHAR)u"\u0014";
+    p       = find_ptr_to_last_character(p_start);
+    q       = decxstr(p, p_start);
+    assert(q == (NULL));
+
+    p_start = (PKMX_WCHAR)u"\u0014\u0014";
+    p       = find_ptr_to_last_character(p_start);
+    q       = decxstr(p, p_start);
+    assert(q == (p - 1));
+
+    p_start = (PKMX_WCHAR)u"\u0014\u0014\u0014";
+    p       = find_ptr_to_last_character(p_start);
+    q       = decxstr(p, p_start);
+    assert(q == (p - 1));
+
+    p_start = (PKMX_WCHAR)u"\u0014\u0014\u0014\u0014";
+    p       = find_ptr_to_last_character(p_start);
+    q       = decxstr(p, p_start);
+    assert(q == (p - 1));
+
+    p_start = (PKMX_WCHAR)u"\u0014\u0014\u0014\u0014\u0014";
+    p       = find_ptr_to_last_character(p_start);
+    q       = decxstr(p, p_start);
+    assert(q == (p - 1));
+
+    p_start = (PKMX_WCHAR)u"\u0014\u0014\u0014\u0014\u0014\u0014";
+    p       = find_ptr_to_last_character(p_start);
+    q       = decxstr(p, p_start);
+    assert(q == (p - 1));
+
+    p_start = (PKMX_WCHAR)u"\uFFFF\u0014";
+    p       = find_ptr_to_last_character(p_start);
+    q       = decxstr(p, p_start);
+    assert(q == (p - 1));
+
+    p_start = (PKMX_WCHAR)u"\uFFFF\u0014\u0014";
+    p       = find_ptr_to_last_character(p_start);
+    q       = decxstr(p, p_start);
+    assert(q == (p-2 ));
+
+    p_start = (PKMX_WCHAR)u"\uFFFF\u0014\u0014\u0014";
+    p       = find_ptr_to_last_character(p_start);
+    q       = decxstr(p, p_start);
+    assert(q == (p - 1));
+
+    p_start = (PKMX_WCHAR)u"\uFFFF\u0014\u0014\u0014\u0014";
+    p       = find_ptr_to_last_character(p_start);
+    q       = decxstr(p, p_start);
+    assert(q == (p - 1));
+
+    p_start = (PKMX_WCHAR)u"\uFFFF\u0014\u0014\u0014\u0014\u0014";
+    p       = find_ptr_to_last_character(p_start);
+    q       = decxstr(p, p_start);
+    assert(q == (p - 5));
+
+    p_start = (PKMX_WCHAR)u"\uFFFF\u0014\u0014\u0014\u0014\u0014\u0014";
+    p       = find_ptr_to_last_character(p_start);
+    q       = decxstr(p, p_start);
+    assert(q == (p - 1));
+
     // -------------------------------------------------------------------------------------------------------------------------------------------------------
     // -- differences in pointer movement for new decxstr ----------------------------------------------------------------------------------------------------
     // ----- OLD version of decxstr: 0x0A not used  => return ( p - 1) , 0x0C not used => return ( p - 1) , 0x0E = 1  => return ( p - 3) 
@@ -1218,7 +1313,7 @@ void test_decxstr() {
   p = (PKMX_WCHAR)u"\uFFFF\u0004\u0062\U0001F609";
   q = incxstr(p);
   assert(q == p + 2);
-}
+  }
 
 constexpr const auto help_str = "\
 test_kmx_xstring [--color]\n\
@@ -1240,4 +1335,4 @@ int main(int argc, char *argv []) {
   test_decxstr();
 
   return 0;
-}
\ No newline at end of file
+}