diff --git a/driver/Makefile.in b/driver/Makefile.in
index 346ce4ab5..f31d76037 100644
--- a/driver/Makefile.in
+++ b/driver/Makefile.in
@@ -38,6 +38,8 @@ CC = @CC@
 INSTALL = @INSTALL@
 INSTALL_PROGRAM = @INSTALL_PROGRAM@
 INSTALL_DATA = @INSTALL_DATA@
+LEX = @LEX@
+YACC = @YACC@
 MAN = @MAN@
 PS2PDF = @PS2PDF@
 
@@ -78,10 +80,10 @@ iverilog@EXEEXT@: $O
 	$(CC) $(LDFLAGS) $O -o iverilog@EXEEXT@ @EXTRALIBS@
 
 cflexor.c: cflexor.lex
-	flex -s -Pcf -ocflexor.c $(srcdir)/cflexor.lex
+	$(LEX) -s -Pcf -ocflexor.c $(srcdir)/cflexor.lex
 
 cfparse.h cfparse.c: cfparse.y
-	bison --verbose -t -d -o cfparse.c --name-prefix=cf $(srcdir)/cfparse.y
+	$(YACC) --verbose -t -d -o cfparse.c --name-prefix=cf $(srcdir)/cfparse.y
 
 %.o: %.c
 	$(CC) $(CPPFLAGS) $(CFLAGS) @DEPENDENCY_FLAG@ -c $< -o $*.o
diff --git a/ivlpp/Makefile.in b/ivlpp/Makefile.in
index f65f1114f..62a799e98 100644
--- a/ivlpp/Makefile.in
+++ b/ivlpp/Makefile.in
@@ -36,6 +36,7 @@ CC = @CC@
 INSTALL = @INSTALL@
 INSTALL_PROGRAM = @INSTALL_PROGRAM@
 INSTALL_DATA = @INSTALL_DATA@
+LEX = @LEX@
 
 ifeq (@srcdir@,.)
 INCLUDE_PATH = -I. -I..
@@ -69,7 +70,7 @@ ivlpp@EXEEXT@: $O
 	$(CC) $(LDFLAGS) $O -o ivlpp@EXEEXT@ @EXTRALIBS@
 
 lexor.c: lexor.lex
-	flex -olexor.c $(srcdir)/lexor.lex
+	$(LEX) -olexor.c $(srcdir)/lexor.lex
 
 install: all installdirs $(libdir)/ivl$(suffix)/ivlpp@EXEEXT@
 
diff --git a/vpi/Makefile.in b/vpi/Makefile.in
index 166c8169e..c15bb3bbe 100644
--- a/vpi/Makefile.in
+++ b/vpi/Makefile.in
@@ -118,12 +118,12 @@ system.vpi: $O $(OPP) ../vvp/libvpi.a
 	$(CXX) @shared@ -o $@ $O $(OPP) -L../vvp $(LDFLAGS) -lvpi $(SYSTEM_VPI_LDFLAGS)
 
 sys_readmem_lex.c: sys_readmem_lex.lex
-	flex -t -Preadmem $(srcdir)/sys_readmem_lex.lex > sys_readmem_lex.c
+	$(LEX) -t -Preadmem $(srcdir)/sys_readmem_lex.lex > sys_readmem_lex.c
 
 sdf_lexor.o: sdf_lexor.c sdf_parse.h
 
 sdf_lexor.c: sdf_lexor.lex
-	flex -t -Psdf $(srcdir)/sdf_lexor.lex > sdf_lexor.c
+	$(LEX) -t -Psdf $(srcdir)/sdf_lexor.lex > sdf_lexor.c
 
 sdf_parse.c sdf_parse.h: $(srcdir)/sdf_parse.y
 	$(YACC) --verbose -d -p sdf -o sdf_parse.c $(srcdir)/sdf_parse.y