diff --git a/common.mk b/common.mk
index 3f508959a7..0242699118 100644
--- a/common.mk
+++ b/common.mk
@@ -47,7 +47,7 @@ RUN_OPTS      = --disable-gems
 # GITPULLOPTIONS = --no-tags
 
 PRISM_SRCDIR = $(srcdir)/prism
-INCFLAGS = -I. -I$(arch_hdrdir) -I$(hdrdir) -I$(srcdir) -I$(PRISM_SRCDIR) -I$(UNICODE_HDR_DIR) $(incflags)
+INCFLAGS = -I. -I$(arch_hdrdir) -I$(ext_hdrdir) -I$(hdrdir) -I$(srcdir) -I$(PRISM_SRCDIR) -I$(UNICODE_HDR_DIR) $(incflags)
 
 GEM_HOME =
 GEM_PATH =
@@ -860,6 +860,9 @@ clean-platform distclean-platform realclean-platform:
 	-$(Q) $(RMDIR) $(PLATFORM_DIR) 2> $(NULL) || $(NULLCMD)
 
 RUBYSPEC_CAPIEXT = spec/ruby/optional/capi/ext
+RUBYSPEC_CAPIEXT_SRCDIR = $(srcdir)/$(RUBYSPEC_CAPIEXT)
+RUBYSPEC_CAPIEXT_DEPS = $(RUBYSPEC_CAPIEXT_SRCDIR)/rubyspec.h $(RUBY_H_INCLUDES) $(LIBRUBY) build-ext
+
 clean-spec: PHONY
 	-$(Q) $(RM) $(RUBYSPEC_CAPIEXT)/*.$(OBJEXT) $(RUBYSPEC_CAPIEXT)/*.$(DLEXT)
 	-$(Q) $(RMDIRS) $(RUBYSPEC_CAPIEXT) 2> $(NULL) || $(NULLCMD)
diff --git a/defs/gmake.mk b/defs/gmake.mk
index c7891674a0..666e057c9d 100644
--- a/defs/gmake.mk
+++ b/defs/gmake.mk
@@ -506,10 +506,10 @@ update-deps:
 
 # order-only-prerequisites doesn't work for $(RUBYSPEC_CAPIEXT)
 # because the same named directory exists in the source tree.
-$(RUBYSPEC_CAPIEXT)/%.$(DLEXT): $(srcdir)/$(RUBYSPEC_CAPIEXT)/%.c $(srcdir)/$(RUBYSPEC_CAPIEXT)/rubyspec.h $(RUBY_H_INCLUDES) $(LIBRUBY)
+$(RUBYSPEC_CAPIEXT)/%.$(DLEXT): $(srcdir)/$(RUBYSPEC_CAPIEXT)/%.c $(RUBYSPEC_CAPIEXT_DEPS)
 	$(ECHO) building $@
 	$(Q) $(MAKEDIRS) $(@D)
-	$(Q) $(DLDSHARED) -L. $(XDLDFLAGS) $(XLDFLAGS) $(LDFLAGS) $(INCFLAGS) -I$(EXTOUT)/include $(CPPFLAGS) $(OUTFLAG)$@ $< $(LIBRUBYARG)
+	$(Q) $(DLDSHARED) -L. $(XDLDFLAGS) $(XLDFLAGS) $(LDFLAGS) $(INCFLAGS) $(CPPFLAGS) $(OUTFLAG)$@ $< $(LIBRUBYARG)
 ifneq ($(POSTLINK),)
 	$(Q) $(POSTLINK)
 endif
@@ -520,7 +520,6 @@ rubyspec-capiext: $(RUBYSPEC_CAPIEXT_SO)
 	@ $(NULLCMD)
 
 ifeq ($(ENABLE_SHARED),yes)
-ruby: $(if $(LIBRUBY_SO_UPDATE),$(RUBYSPEC_CAPIEXT_SO))
 exts: rubyspec-capiext
 endif
 
diff --git a/template/Makefile.in b/template/Makefile.in
index 743971abcb..aed81bf1ef 100644
--- a/template/Makefile.in
+++ b/template/Makefile.in
@@ -77,7 +77,8 @@ DOCTARGETS = @RDOCTARGET@ @CAPITARGET@
 
 EXTOUT = @EXTOUT@
 TIMESTAMPDIR  = $(EXTOUT)/.timestamp
-arch_hdrdir = $(EXTOUT)/include/$(arch)
+ext_hdrdir = $(EXTOUT)/include
+arch_hdrdir = $(ext_hdrdir)/$(arch)
 VPATH = $(arch_hdrdir)/ruby:$(hdrdir)/ruby:$(srcdir):$(srcdir)/missing
 
 empty =
diff --git a/win32/Makefile.sub b/win32/Makefile.sub
index 3acdb1a2bd..80225c3063 100644
--- a/win32/Makefile.sub
+++ b/win32/Makefile.sub
@@ -493,7 +493,8 @@ ENCOBJS = dmyenc.$(OBJEXT)
 EXTOBJS = dmyext.$(OBJEXT)
 !endif
 
-arch_hdrdir = $(EXTOUT)/include/$(arch)
+ext_hdrdir = $(EXTOUT)/include
+arch_hdrdir = $(ext_hdrdir)/$(arch)
 top_srcdir = $(srcdir)
 hdrdir = $(srcdir)/include
 VPATH = $(arch_hdrdir)/ruby;$(hdrdir)/ruby;$(srcdir);$(srcdir)/missing;$(win_srcdir)
@@ -1468,8 +1469,6 @@ loadpath: verconf.h
 	sed -e '1,/^const char ruby_initial_load_paths/d;/;/,$$d' \
 	    -e '/^^ /!d;s/ *"\\\\0"$$//;s/" *"//g'
 
-RUBYSPEC_CAPIEXT_SRCDIR = $(srcdir)/$(RUBYSPEC_CAPIEXT)
-RUBYSPEC_CAPIEXT_DEPS = $(RUBYSPEC_CAPIEXT_SRCDIR)/rubyspec.h $(RUBY_H_INCLUDES) $(LIBRUBY)
 RUBYSPEC_CAPIEXT_EXTS =
 
 !if [echo>rubyspec-capiext.mk RUBYSPEC_CAPIEXT_EXTS = \]