diff --git a/test/ref/Makefile b/test/ref/Makefile
index 09dd96d44..6f0bd1bc1 100644
--- a/test/ref/Makefile
+++ b/test/ref/Makefile
@@ -1,4 +1,3 @@
-
 # makefile for the regression tests that generate output which has to be
 # compared with reference output
 
@@ -24,7 +23,7 @@ WORKDIR := ..$S..$Stestwrk
 DIFF := $(WORKDIR)/bdiff
 
 CC := gcc
-CFLAGS := -O2 -Wall -W -Wextra -fwrapv -fno-strict-overflow
+CFLAGS := -O2 -Wall -W -Wextra -funsigned-char -fwrapv -fno-strict-overflow
 
 .PHONY: all clean
 
@@ -34,6 +33,11 @@ TESTS := $(foreach option,. .o. .os. .osi. .osir. .oi. .oir. .or.,$(SOURCES:%.c=
 
 all: $(REFS) $(TESTS)
 
+# "yaccdbg.c" includes "yacc.c".
+# yaccdbg's built files must depend on both of them.
+
+$(WORKDIR)/yaccdbg.ref: yacc.c
+
 $(WORKDIR)/%.ref: %.c
 	$(CC) $(CFLAGS) $< -o $(WORKDIR)/$*.host
 	$(WORKDIR)$S$*.host > $@
@@ -48,6 +52,8 @@ $(WORKDIR)/switch.%rg: CC65FLAGS += -Wc --all-cdecl
 $(WORKDIR)/yacc.%rg: CC65FLAGS += -Wc --all-cdecl
 $(WORKDIR)/yaccdbg%prg: CC65FLAGS += -Wc --all-cdecl
 
+$(WORKDIR)/yaccdbg%prg: yacc.c
+
 $(WORKDIR)/%.prg: %.c $(WORKDIR)/%.ref
 	$(CL65) $(CC65FLAGS) $< -o $@
 	$(SIM65) $(SIM65FLAGS) $@ > $(WORKDIR)/$*.out
diff --git a/test/ref/yacc.c b/test/ref/yacc.c
index 5768f80d0..d0b9190e4 100644
--- a/test/ref/yacc.c
+++ b/test/ref/yacc.c
@@ -562,7 +562,7 @@ yylook()
 		}
 
 # ifdef LEXDEBUG
-		if((*(lsp-1)-yysvec-1)<0)
+		if (*(lsp-1) < yysvec + 1)
 		{
 			fprintf(yyout,"yylook:  stopped (end)\n");
 		}