diff --git a/src/ExprIntrp/ExprIntrp.lex b/src/ExprIntrp/ExprIntrp.lex
index 26df2a2798..3654fe71d1 100755
--- a/src/ExprIntrp/ExprIntrp.lex
+++ b/src/ExprIntrp/ExprIntrp.lex
@@ -37,6 +37,7 @@ void ExprIntrp_start_string(char* str)
 void ExprIntrp_stop_string()
 {
   ExprIntrp_delete_buffer(ExprIntrp_bufstring);
+  ExprIntrp_bufstring = (YY_BUFFER_STATE) 0;
 }
 
 int yywrap()
diff --git a/src/QABugs/QABugs_11.cxx b/src/QABugs/QABugs_11.cxx
old mode 100644
new mode 100755
index 8f11173c1e..c17eec4ce1
--- a/src/QABugs/QABugs_11.cxx
+++ b/src/QABugs/QABugs_11.cxx
@@ -5330,6 +5330,29 @@ Standard_Integer bcarray (Draw_Interpretor& di, Standard_Integer argc, const cha
   return 0;
 }
 
+#include <ExprIntrp_GenExp.hxx>
+Standard_Integer CR23403 (Draw_Interpretor& di, Standard_Integer argc, const char ** argv)
+{
+	
+  if (argc != 2) {
+    di << "Usage : " << argv[0] << " string\n";
+    return 1;
+  }
+
+  Standard_CString aString = argv[1];
+  Handle(ExprIntrp_GenExp) myExpr = ExprIntrp_GenExp::Create();
+  try {
+    OCC_CATCH_SIGNALS
+    myExpr->Process( aString );
+  }
+  catch(Standard_Failure) {
+    Handle(Standard_Failure) aFail = Standard_Failure::Caught();
+    di << "Exception : " << aFail->GetMessageString() << "\n";
+  }
+
+  return 0;
+}
+
 void QABugs::Commands_11(Draw_Interpretor& theCommands) {
   const char *group = "QABugs";
 
@@ -5439,5 +5462,6 @@ void QABugs::Commands_11(Draw_Interpretor& theCommands) {
   theCommands.Add("bcarray", "bcarray", __FILE__, bcarray, group);
   theCommands.Add("OCC22762", "OCC22762 x1 y1 z1 x2 y2 z3", __FILE__, OCC22762, group);
   theCommands.Add("OCC22558", "OCC22558 x_vec y_vec z_vec x_dir y_dir z_dit x_pnt y_pnt z_pnt", __FILE__, OCC22558, group);
+  theCommands.Add("CR23403", "CR23403 string", __FILE__, CR23403, group);
   return;
 }
diff --git a/tests/bugs/demo/CR23410 b/tests/bugs/demo/CR23410
index 2949ea2bcb..2a4b9ec643 100755
--- a/tests/bugs/demo/CR23410
+++ b/tests/bugs/demo/CR23410
@@ -7,9 +7,12 @@ puts ""
 #######################################################################
 pload QAcommands
 
-set R_check 0.45098000764846802
-set G_check 1
-set B_check 0.066666000000000003
+set r_1 0.4
+set r_2 0.5
+set g_1 0.9
+set g_2 1
+set b_1 0
+set b_2 0.1
 set x1 128
 set y1 235
 box result 100 100 100
@@ -22,7 +25,28 @@ regexp {RED +: +([-0-9.+eE]+)} $color full rd
 regexp {GREEN +: +([-0-9.+eE]+)} $color full gr
 regexp {BLUE +: +([-0-9.+eE]+)} $color full bl
 
-if { $rd != $R_check || $gr != $G_check || $bl != $B_check} {
+set red_status 0
+if { $rd < $r_1 || $rd > $r_2 } {
+    set red_status 1
+} else {
+    set red_status 0
+}
+
+set green_status 0
+if { $gr < $g_1 || $gr > $g_2 } {
+    set green_status 1
+} else {
+    set green_status 0
+}
+
+set blue_status 0
+if { $bl < $b_1 || $bl > $b_2 } {
+    set blue_status 1
+} else {
+    set blue_status 0
+}
+
+if { $red_status != 0 || $green_status != 0 || $blue_status != 0 } {
     puts "Error : color are not equal"
     puts "Error : QA command QAGetPixelColor doesn't work properly"
 }
diff --git a/tests/bugs/fclasses/CR23403 b/tests/bugs/fclasses/CR23403
new file mode 100755
index 0000000000..b3b65a6e68
--- /dev/null
+++ b/tests/bugs/fclasses/CR23403
@@ -0,0 +1,12 @@
+#######################################################################
+# Crash when parsing an expression with lexical error
+#######################################################################
+pload QAcommands
+
+set result [CR23403 \t]
+set length [llength ${result}]
+
+puts ""
+if { ${length} != 0 } {
+  puts "Error : parsing is incorrect"
+}
\ No newline at end of file
diff --git a/tests/bugs/grids.list b/tests/bugs/grids.list
index 21bd88e754..edfa79ce12 100755
--- a/tests/bugs/grids.list
+++ b/tests/bugs/grids.list
@@ -1,6 +1,8 @@
 001 demo
-002 iges
-003 xde
+002 fclasses
+003 iges
+004 xde
+