--- a/Makefile.in
+++ b/Makefile.in
@@ -78,6 +78,7 @@ HOSTCC = @CC@
 HOSTCFLAGS = @WARNING_FLAGS@ @WARNING_FLAGS_CC@ @CFLAGS@
 
 BUILDCC = @CC_FOR_BUILD@
+BUILD_CFLAGS = -O2
 BUILDEXT = @BUILD_EXEEXT@
 CC = @CC@
 CXX = @CXX@
@@ -139,7 +140,7 @@ all: dep config.h _pli_types.h version_t
 ifeq (@MINGW32@,yes)
 all: dosify$(BUILDEXT)
 dosify$(BUILDEXT): $(srcdir)/dosify.c
-	$(BUILDCC) $(CPPFLAGS) $(CFLAGS) $(LDFLAGS) -o dosify$(BUILDEXT) $(srcdir)/dosify.c
+	$(BUILDCC) $(BUILD_CFLAGS) -o dosify$(BUILDEXT) $(srcdir)/dosify.c
 endif
 
 # This rule rules the compiler in the trivial hello.vl program to make
@@ -250,7 +251,7 @@ iverilog-vpi: $(srcdir)/iverilog-vpi.sh
 endif
 
 version.exe: $(srcdir)/version.c $(srcdir)/version_base.h version_tag.h
-	$(BUILDCC) $(CPPFLAGS) $(CFLAGS) $(LDFLAGS) -o version.exe -I. -I$(srcdir) $(srcdir)/version.c
+	$(BUILDCC) $(BUILD_CFLAGS) -o version.exe -I. -I$(srcdir) $(srcdir)/version.c
 
 %.o: %.cc config.h
 	$(CXX) $(CPPFLAGS) $(CXXFLAGS) @DEPENDENCY_FLAG@ -c $< -o $*.o
--- a/vvp/Makefile.in
+++ b/vvp/Makefile.in
@@ -39,6 +39,7 @@ HOSTCC = @CC@
 HOSTCFLAGS = @WARNING_FLAGS@ @WARNING_FLAGS_CC@ @CFLAGS@
 
 BUILDCC = @CC_FOR_BUILD@
+BUILD_CFLAGS = -O2
 BUILDEXT = @BUILD_EXEEXT@
 CXX = @CXX@
 INSTALL = @INSTALL@
@@ -168,7 +169,7 @@ endif
 	mv $*.d dep/$*.d
 
 tables.cc: $(srcdir)/draw_tt.c
-	$(BUILDCC) $(CPPFLAGS) $(CFLAGS) $(LDFLAGS) -o draw_tt$(BUILDEXT) $(srcdir)/draw_tt.c
+	$(BUILDCC) $(BUILD_CFLAGS) -o draw_tt$(BUILDEXT) $(srcdir)/draw_tt.c
 	./draw_tt$(BUILDEXT) > tables.cc
 	rm draw_tt$(BUILDEXT)