diff --git a/ChangeLog b/ChangeLog
index f5ce0ee3b4..e78e7dd621 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,4 +1,6 @@
-Thu Nov 11 21:46:17 2010  Nobuyoshi Nakada  <nobu@ruby-lang.org>
+Thu Nov 11 21:47:12 2010  Nobuyoshi Nakada  <nobu@ruby-lang.org>
+
+	* common.mk (SHOWFLAGS): show compile flags.
 
 	* common.mk: hide long command lines by default.  verbose-mode is
 	  turned on by V=1 as before.
diff --git a/common.mk b/common.mk
index ab8e1a556f..75d555cad3 100644
--- a/common.mk
+++ b/common.mk
@@ -139,6 +139,16 @@ all: main docs
 main: encs exts
 	@$(RUNCMD) $(MKMAIN_CMD) $(MAKE)
 
+.PHONY: showflags SHOWFLAGS
+exts enc trans: showflags
+showflags: SHOWFLAGS
+SHOWFLAGS:
+	@echo "	CFLAGS = $(CFLAGS)"
+	@echo "	XCFLAGS = $(XCFLAGS)"
+	@echo "	CPPFLAGS = $(CPPFLAGS)"
+	@echo "	DLDFLAGS = $(DLDFLAGS)"
+	@echo "	SOLIBS = $(SOLIBS)"
+
 exts: $(MKMAIN_CMD)
 
 $(MKMAIN_CMD): $(MKFILES) incs $(PREP) $(RBCONFIG) $(LIBRUBY)