diff --git a/ext/extmk.rb b/ext/extmk.rb
index 39cbce1bc9fe68..888eba6c676d41 100755
--- a/ext/extmk.rb
+++ b/ext/extmk.rb
@@ -43,6 +43,7 @@ def self.target_rbconfig
 
 $topdir = "."
 $top_srcdir = srcdir
+$extmk = true
 inplace = File.identical?($top_srcdir, $topdir)
 
 $" << "mkmf.rb"
diff --git a/prism/srcs.mk b/prism/srcs.mk
index 565d793cc0a210..ff4ddff0722e32 100644
--- a/prism/srcs.mk
+++ b/prism/srcs.mk
@@ -4,9 +4,8 @@ PRISM_CONFIG = $(PRISM_SRCDIR)/config.yml
 
 srcs uncommon.mk: prism/.srcs.mk.time
 
-prism/.srcs.mk.time:
+prism/.srcs.mk.time: $(order_only) $(PRISM_BUILD_DIR)/.time
 prism/$(HAVE_BASERUBY:no=.srcs.mk.time):
-	mkdir -p $(@D)
 	touch $@
 prism/$(HAVE_BASERUBY:yes=.srcs.mk.time): \
 		$(PRISM_SRCDIR)/templates/template.rb \
diff --git a/prism/srcs.mk.in b/prism/srcs.mk.in
index 0b921b7f0bb07d..e337eff8ea00e5 100644
--- a/prism/srcs.mk.in
+++ b/prism/srcs.mk.in
@@ -12,9 +12,8 @@ PRISM_CONFIG = $(PRISM_SRCDIR)/config.yml
 
 srcs <%=%><%=mk%>: prism/.srcs.mk.time
 
-prism/.srcs.mk.time:
+prism/.srcs.mk.time: $(order_only) $(PRISM_BUILD_DIR)/.time
 prism/$(HAVE_BASERUBY:no=.srcs.mk.time):
-	mkdir -p $(@D)
 	touch $@
 prism/$(HAVE_BASERUBY:yes=.srcs.mk.time): \
 		$(PRISM_SRCDIR)/templates/template.rb \