--- a/PEG/Flex.pri
+++ b/PEG/Flex.pri
@@ -1,5 +1,6 @@
 flex.name = Flex ${QMAKE_FILE_IN}
 flex.input = FLEX_SOURCES
+flex.depends = ${QMAKE_FILE_PATH}/${QMAKE_FILE_BASE}.parser.cpp
 flex.output = ${QMAKE_FILE_PATH}/${QMAKE_FILE_BASE}.lexer.cpp
 
 win32:flex.commands = win_flex --wincompat -o ${QMAKE_FILE_PATH}/${QMAKE_FILE_BASE}.lexer.cpp ${QMAKE_FILE_IN}