diff --git a/Makefile.in b/Makefile.in
index 5c9e83320..fa578b147 100644
--- a/Makefile.in
+++ b/Makefile.in
@@ -16,7 +16,7 @@
 #    59 Temple Place - Suite 330
 #    Boston, MA 02111-1307, USA
 #
-#ident "$Id: Makefile.in,v 1.109 2001/12/06 02:55:24 steve Exp $"
+#ident "$Id: Makefile.in,v 1.110 2001/12/30 17:20:33 steve Exp $"
 #
 #
 SHELL = /bin/sh
@@ -46,6 +46,8 @@ INSTALL_SCRIPT = @INSTALL_SCRIPT@
 INSTALL_PROGRAM = @INSTALL_PROGRAM@
 INSTALL_DATA = @INSTALL_DATA@
 STRIP = @STRIP@
+LEX = @LEX@
+YACC = @YACC@
 
 CPPFLAGS = @CPPFLAGS@ @DEFS@
 CXXFLAGS = @CXXFLAGS@ -I. -I$(srcdir)
@@ -170,14 +172,14 @@ lexor.o: lexor.cc parse.h
 parse.o: parse.cc
 
 parse.h parse.cc: $(srcdir)/parse.y
-	bison --verbose -t -p VL -d -o parse.cc $(srcdir)/parse.y
+	$(YACC) --verbose -t -p VL -d -o parse.cc $(srcdir)/parse.y
 	mv parse.cc.h parse.h || mv parse.hh parse.h
 
 syn-rules.cc: $(srcdir)/syn-rules.y
-	bison --verbose -p syn_ -o syn-rules.cc $(srcdir)/syn-rules.y
+	$(YACC) --verbose -p syn_ -o syn-rules.cc $(srcdir)/syn-rules.y
 
 lexor.cc: $(srcdir)/lexor.lex
-	flex -PVL -s -olexor.cc $(srcdir)/lexor.lex
+	$(LEX) -PVL -s -olexor.cc $(srcdir)/lexor.lex
 
 lexor_keyword.o: lexor_keyword.cc
 
diff --git a/configure.in b/configure.in
index 62a899251..c453b069e 100644
--- a/configure.in
+++ b/configure.in
@@ -14,6 +14,22 @@ then
         exit 1
 fi
 
+AC_CHECK_PROGS(LEX,flex,none)
+if test "$LEX" = "none"
+then
+	echo "*** Error: No suitable flex found. ***"
+        echo "    Please install the 'flex' package."
+        exit 1
+fi
+
+AC_CHECK_PROGS(YACC,bison,none)
+if test "$YACC" = "none"
+then
+	echo "*** Error: No suitable bison found. ***"
+        echo "    Please install the 'bison' package."
+        exit 1
+fi
+
 AC_LANG_CPLUSPLUS
 
 AC_CHECK_HEADERS(getopt.h malloc.h iosfwd sys/wait.h)
diff --git a/vvp/Makefile.in b/vvp/Makefile.in
index 05be187c4..3d904ad3d 100644
--- a/vvp/Makefile.in
+++ b/vvp/Makefile.in
@@ -16,7 +16,7 @@
 #    59 Temple Place - Suite 330
 #    Boston, MA 02111-1307, USA
 #
-#ident "$Id: Makefile.in,v 1.32 2001/11/10 18:07:11 steve Exp $"
+#ident "$Id: Makefile.in,v 1.33 2001/12/30 17:20:33 steve Exp $"
 #
 #
 SHELL = /bin/sh
@@ -39,6 +39,8 @@ INSTALL_SCRIPT = @INSTALL_SCRIPT@
 INSTALL_PROGRAM = @INSTALL_PROGRAM@
 INSTALL_DATA = @INSTALL_DATA@
 STRIP = @STRIP@
+LEX = @LEX@
+YACC = @YACC@
 
 CPPFLAGS = -I. -I$(srcdir)/.. @CPPFLAGS@ @DEFS@ -DMODULE_DIR=\"$(libdir)/ivl\"
 CXXFLAGS = @CXXFLAGS@
@@ -88,11 +90,11 @@ parse.o: parse.cc
 tables.o: tables.cc
 
 parse.h parse.cc: $(srcdir)/parse.y
-	bison --verbose -t -d -o parse.cc $(srcdir)/parse.y
+	$(YACC) --verbose -t -d -o parse.cc $(srcdir)/parse.y
 	mv parse.cc.h parse.h
 
 lexor.cc: $(srcdir)/lexor.lex
-	flex -s -olexor.cc $(srcdir)/lexor.lex
+	$(LEX) -s -olexor.cc $(srcdir)/lexor.lex
 
 vvp.pdf: $(srcdir)/vvp.man
 	man -t $(srcdir)/vvp.man | ps2pdf - vvp.pdf
diff --git a/vvp/configure.in b/vvp/configure.in
index 118ad1356..049cc952a 100644
--- a/vvp/configure.in
+++ b/vvp/configure.in
@@ -10,6 +10,22 @@ AC_EXEEXT
 AC_MINGW32
 AC_SUBST(EXEEXT)
 
+AC_CHECK_PROGS(LEX,flex,none)
+if test "$LEX" = "none"
+then
+	echo "*** Error: No suitable flex found. ***"
+        echo "    Please install the 'flex' package."
+        exit 1
+fi
+
+AC_CHECK_PROGS(YACC,bison,none)
+if test "$YACC" = "none"
+then
+	echo "*** Error: No suitable bison found. ***"
+        echo "    Please install the 'bison' package."
+        exit 1
+fi
+
 AC_PROG_INSTALL
 
 AC_ARG_ENABLE(vvp-debug, vvp-debug -- interactive debugger for VVP runtime.,