diff --git a/libyul/AsmParser.cpp b/libyul/AsmParser.cpp
index 69c43563b..ce25724f9 100644
--- a/libyul/AsmParser.cpp
+++ b/libyul/AsmParser.cpp
@@ -131,11 +131,13 @@ void Parser::fetchSourceLocationFromComment()
 		m_locationOverride = SourceLocation{};
 		if (!sourceIndex || !start || !end)
 			m_errorReporter.syntaxError(6367_error, commentLocation, "Invalid value in source location mapping. Could not parse location specification.");
-		else if (!((start < 0 && end < 0) || (start >= 0 && *start <= *end)))
+		else if (!((*start < 0 && *end < 0) || (*start >= 0 && *start <= *end)))
 			m_errorReporter.syntaxError(5798_error, commentLocation, "Invalid value in source location mapping. Start offset larger than end offset.");
+		else if (sourceIndex == -1 && (0 <= *start && *start <= *end)) // Use source index -1 to indicate original source.
+			m_locationOverride = SourceLocation{*start, *end, ParserBase::currentLocation().source};
 		else if (!(sourceIndex >= 0 && m_charStreamMap->count(static_cast<unsigned>(*sourceIndex))))
 			m_errorReporter.syntaxError(2674_error, commentLocation, "Invalid source mapping. Source index not defined via @use-src.");
-		else if (sourceIndex >= 0)
+		else
 		{
 			shared_ptr<CharStream> charStream = m_charStreamMap->at(static_cast<unsigned>(*sourceIndex));
 			solAssert(charStream, "");
diff --git a/test/libyul/Parser.cpp b/test/libyul/Parser.cpp
index 7fe43f842..84f9f8045 100644
--- a/test/libyul/Parser.cpp
+++ b/test/libyul/Parser.cpp
@@ -556,6 +556,28 @@ BOOST_AUTO_TEST_CASE(customSourceLocations_ensure_last_match)
 	CHECK_LOCATION(varDecl.debugData->location, sourceText, 30, 40);
 }
 
+BOOST_AUTO_TEST_CASE(customSourceLocations_reference_original_sloc)
+{
+	ErrorList errorList;
+	ErrorReporter reporter(errorList);
+	auto const sourceText = R"(
+		/// @src 1:2:3
+		{
+			/// @src -1:10:20
+			let x:bool := true
+		}
+	)";
+	EVMDialectTyped const& dialect = EVMDialectTyped::instance(EVMVersion{});
+	shared_ptr<Block> result = parse(sourceText, dialect, reporter);
+	BOOST_REQUIRE(!!result);
+	BOOST_REQUIRE(holds_alternative<VariableDeclaration>(result->statements.at(0)));
+	VariableDeclaration const& varDecl = get<VariableDeclaration>(result->statements.at(0));
+
+	// -1 points to original source code, which in this case is `sourceText` (which is also
+	// available via `0`, that's why the first @src is set to `1` instead.)
+	CHECK_LOCATION(varDecl.debugData->location, sourceText, 10, 20);
+}
+
 BOOST_AUTO_TEST_SUITE_END()
 
 } // end namespaces