diff --git a/vpi/Makefile.in b/vpi/Makefile.in
index ea04009b5..82b0a9094 100644
--- a/vpi/Makefile.in
+++ b/vpi/Makefile.in
@@ -94,8 +94,13 @@ distclean: clean
 	rm -f Makefile config.log
 	rm -f vpi_config.h stamp-vpi_config-h
 
+# The -U flag is used to skip checking paths that depend on that define having
+# an explict value (i.e. the define is expected to be real code).
 cppcheck: $(O:.o=.c) $(OPP:.o=.cc) $(M:.o=.c) $(V:.o=.c)
 	cppcheck --enable=all -f --suppressions-list=$(srcdir)/cppcheck.sup \
+	         -UYY_USER_INIT \
+	         -UYYPARSE_PARAM -UYYPRINT -Ushort -Uyyoverflow \
+	         -UYYTYPE_INT8 -UYYTYPE_INT16 -UYYTYPE_UINT8 -UYYTYPE_UINT16 \
 	         --relative-paths=$(srcdir) $(INCLUDE_PATH) $^
 
 Makefile: $(srcdir)/Makefile.in ../config.status
diff --git a/vpi/lxt2_write.c b/vpi/lxt2_write.c
index 38b11f602..c1fed8a43 100644
--- a/vpi/lxt2_write.c
+++ b/vpi/lxt2_write.c
@@ -578,13 +578,13 @@ return;
 
 static void lxt2_wr_emitfacs(struct lxt2_wr_trace *lt)
 {
-int i;
+unsigned int i;
 
 if((lt)&&(lt->numfacs))
 	{
 	struct lxt2_wr_symbol *s = lt->symchain;
 	struct lxt2_wr_symbol **aliascache = calloc(lt->numalias ? lt->numalias : 1, sizeof(struct lxt2_wr_symbol *));
-	int aliases_encountered, facs_encountered;
+	unsigned int aliases_encountered, facs_encountered;
 
 	lt->sorted_facs = (struct lxt2_wr_symbol **)calloc(lt->numfacs, sizeof(struct lxt2_wr_symbol *));
 
@@ -1369,7 +1369,7 @@ if((lt->timegranule>=lt->maxgranule)||(do_finalize)||(early_flush))
 	for(i=0;i<lt->num_map_entries;i++)
 		{
 		/* fprintf(stderr, "+++ %08x (%d)(%d)\n", dt->item, i, dt->val); */
-		if(dt->val != i)
+		if(((unsigned int)dt->val) != i)
 			{
 			fprintf(stderr, "internal error line %d\n", __LINE__);
 			exit(255);
diff --git a/vpi/lxt2_write.h b/vpi/lxt2_write.h
index 8c9a47b68..7f2c6d134 100644
--- a/vpi/lxt2_write.h
+++ b/vpi/lxt2_write.h
@@ -163,7 +163,7 @@ off_t current_chunk, current_chunkz;
 struct lxt2_wr_symbol *sym[LXT2_WR_SYMPRIME];
 struct lxt2_wr_symbol **sorted_facs;
 struct lxt2_wr_symbol *symchain;
-int numfacs, numalias;
+unsigned int numfacs, numalias;
 int numfacbytes;
 int longestname;
 
@@ -174,7 +174,7 @@ lxttime_t mintime, maxtime;
 lxtstime_t timezero;
 unsigned int timegranule;
 int timescale;
-int timepos;
+unsigned int timepos;
 unsigned int maxgranule;
 lxttime_t firsttime, lasttime;
 lxttime_t timetable[LXT2_WR_GRANULE_SIZE];