diff --git a/common.mk b/common.mk
index b558d3619d..dd11e27d5e 100644
--- a/common.mk
+++ b/common.mk
@@ -779,7 +779,9 @@ common-srcs: {$(VPATH)}parse.c {$(VPATH)}lex.c {$(VPATH)}enc/trans/newline.c {$(
 srcs: common-srcs srcs-enc
 
 EXT_SRCS = $(srcdir)/ext/ripper/ripper.c \
-	   $(srcdir)/ext/rbconfig/sizeof/sizes.c
+	   $(srcdir)/ext/rbconfig/sizeof/sizes.c \
+	   $(srcdir)/ext/socket/constdefs.c \
+	   # EXT_SRCS
 
 srcs-ext: $(EXT_SRCS)
 
@@ -890,6 +892,12 @@ $(srcdir)/ext/rbconfig/sizeof/sizes.c: $(srcdir)/ext/rbconfig/sizeof/depend \
 	$(exec) $(MAKE) -f - $(MFLAGS) \
 		Q=$(Q) ECHO=$(ECHO) top_srcdir=../../.. srcdir=. VPATH=../../.. RUBY="$(BASERUBY)"
 
+$(srcdir)/ext/socket/constdefs.c: $(srcdir)/ext/socket/depend
+	$(Q) $(CHDIR) $(@D) && \
+	sed -n '/^constdefs/,/^$$/p' depend | \
+	$(exec) $(MAKE) -f - $(MFLAGS) constdefs.h constdefs.c \
+		Q=$(Q) ECHO=$(ECHO) top_srcdir=../../.. srcdir=. VPATH=../../.. RUBY="$(BASERUBY)"
+
 ##
 
 run: fake miniruby$(EXEEXT) PHONY