diff --git a/src/gsi/gsi/gsiTypes.h b/src/gsi/gsi/gsiTypes.h
index cf02ea391..974ded2ec 100644
--- a/src/gsi/gsi/gsiTypes.h
+++ b/src/gsi/gsi/gsiTypes.h
@@ -35,6 +35,9 @@
 #include <set>
 #include <stdexcept>
 #include <cstdint>
+#if __cplusplus >= 201703L
+#include <optional>
+#endif
 
 #if defined(HAVE_QT)
 #include <QString>
diff --git a/src/gsi/unit_tests/gsiExpressionTests.cc b/src/gsi/unit_tests/gsiExpressionTests.cc
index 2f83ffce0..d85f566fe 100644
--- a/src/gsi/unit_tests/gsiExpressionTests.cc
+++ b/src/gsi/unit_tests/gsiExpressionTests.cc
@@ -748,28 +748,28 @@ TEST(14)
     v = e.parse("var t = CplxTrans.new(1.5, 2.5); var tt = CplxTrans.new(); t.assign(other=t)").execute();
     EXPECT_EQ (true, false);
   } catch (tl::Exception &ex) {
-    EXPECT_EQ (ex.msg ().find ("Keyword arguments not permitted at position 60 (...assign(other=t))"), 0);
+    EXPECT_EQ (ex.msg ().find ("Keyword arguments not permitted at position 60 (...assign(other=t))"), size_t (0));
   }
 
   try {
     v = e.parse("var t = CplxTrans.new('abc');").execute();
     EXPECT_EQ (true, false);
   } catch (tl::Exception &ex) {
-    EXPECT_EQ (ex.msg ().find ("No overload with matching arguments. Variants are:"), 0);
+    EXPECT_EQ (ex.msg ().find ("No overload with matching arguments. Variants are:"), size_t (0));
   }
 
   try {
     v = e.parse("var t = CplxTrans.new(uu=17);").execute();
     EXPECT_EQ (true, false);
   } catch (tl::Exception &ex) {
-    EXPECT_EQ (ex.msg ().find ("Can't match arguments. Variants are:"), 0);
+    EXPECT_EQ (ex.msg ().find ("Can't match arguments. Variants are:"), size_t (0));
   }
 
   try {
     v = e.parse("var t = CplxTrans.new(u='17');").execute();
     EXPECT_EQ (true, false);
   } catch (tl::Exception &ex) {
-    EXPECT_EQ (ex.msg ().find ("No overload with matching arguments. Variants are:"), 0);
+    EXPECT_EQ (ex.msg ().find ("No overload with matching arguments. Variants are:"), size_t (0));
   }
 }
 
diff --git a/src/tl/tl/tlXMLParser.cc b/src/tl/tl/tlXMLParser.cc
index 164578ab0..55174fc75 100644
--- a/src/tl/tl/tlXMLParser.cc
+++ b/src/tl/tl/tlXMLParser.cc
@@ -75,7 +75,7 @@ public:
     mp_progress->set_unit (1024 * 1024);
   }
 
-  size_t read (char *data, size_t n)
+  int read (char *data, size_t n)
   {
     try {
 
@@ -88,11 +88,7 @@ public:
         *data++ = *rd;
       }
 
-      if (n0 == n) {
-        return -1;
-      } else {
-        return n0 - n;
-      }
+      return int (n0 - n);
 
     } catch (tl::Exception &ex) {
       m_error = ex.msg ();
@@ -279,27 +275,24 @@ public:
     XML_SetElementHandler (mp_parser, start_element_handler, end_element_handler);
     XML_SetCharacterDataHandler (mp_parser, cdata_handler);
 
-    const size_t chunk = 65536;
+    const int chunk = 65536;
     char buffer [chunk];
 
-    size_t n;
+    int n;
 
     do {
 
-      try {
+      n = source.source ()->read (buffer, chunk);
+      if (n < 0) {
+        break;
+      }
 
-        n = source.source ()->read (buffer, chunk);
-
-        XML_Status status = XML_Parse (mp_parser, buffer, int (n), n < chunk /*is final*/);
-        if (status == XML_STATUS_ERROR) {
-          m_has_error = true;
-          m_error = XML_ErrorString (XML_GetErrorCode (mp_parser));
-          m_error_line = XML_GetErrorLineNumber (mp_parser);
-          m_error_column = XML_GetErrorColumnNumber (mp_parser);
-        }
-
-      } catch (tl::Exception &ex) {
-        error (ex);
+      XML_Status status = XML_Parse (mp_parser, buffer, n, n < chunk /*is final*/);
+      if (status == XML_STATUS_ERROR) {
+        m_has_error = true;
+        m_error = XML_ErrorString (XML_GetErrorCode (mp_parser));
+        m_error_line = XML_GetErrorLineNumber (mp_parser);
+        m_error_column = XML_GetErrorColumnNumber (mp_parser);
       }
 
     } while (n == chunk && !m_has_error);
@@ -343,7 +336,7 @@ void end_element_handler (void *user_data, const XML_Char *name)
 void cdata_handler (void *user_data, const XML_Char *s, int len)
 {
   XMLParserPrivateData *d = reinterpret_cast<XMLParserPrivateData *> (user_data);
-  d->cdata (std::string (s, 0, size_t (len)));
+  d->cdata (std::string (s, size_t (len)));
 }