diff --git a/src/colorer/parsers/TextParserImpl.cpp b/src/colorer/parsers/TextParserImpl.cpp
index 7f9335a..8d51b17 100644
--- a/src/colorer/parsers/TextParserImpl.cpp
+++ b/src/colorer/parsers/TextParserImpl.cpp
@@ -521,8 +521,13 @@ bool TextParser::Impl::colorize(CRegExp* root_end_re, bool lowContentPriority)
       clearLine = current_parse_line;
       str = lineSource->getLine(current_parse_line);
       if (str == nullptr) {
-        throw Exception("null String passed into the parser: " +
-                        UStr::to_unistr(current_parse_line));
+        // LineSource can return null if the line is not available (e.g. editor shutdown).
+        // Stop parsing gracefully instead of throwing across threads.
+        str = nullptr;
+        clearLine = -1;
+        endLine = current_parse_line;
+        stackLevel--;
+        return true;
       }
       regionHandler->clearLine(current_parse_line, str);
     }
diff --git a/src/colorer/strings/legacy/UnicodeString.cpp b/src/colorer/strings/legacy/UnicodeString.cpp
index 227d4a3..bb3873c 100644
--- a/src/colorer/strings/legacy/UnicodeString.cpp
+++ b/src/colorer/strings/legacy/UnicodeString.cpp
@@ -3,6 +3,7 @@
 #include <colorer/strings/legacy/Encodings.h>
 #include <colorer/strings/legacy/UnicodeString.h>
 #include <cstdlib>
+#include <string>
 #include "colorer/Exception.h"
 
 UnicodeString operator+(const UnicodeString& s1, const UnicodeString& s2)
@@ -90,7 +91,8 @@ UnicodeString::UnicodeString(const UnicodeString& cstring, int32_t s, int32_t l)
 
 UnicodeString::UnicodeString(int no)
 {
-  CString dtext = CString(std::to_string(no).c_str());
+  const std::string number_text = std::to_string(no);
+  CString dtext = CString(number_text.c_str());
   construct(&dtext, 0, npos);
 }