diff --git a/ext/zlib/extconf.rb b/ext/zlib/extconf.rb
index 71bcc577d1..c3035e37b5 100644
--- a/ext/zlib/extconf.rb
+++ b/ext/zlib/extconf.rb
@@ -85,7 +85,7 @@ if have_zlib
         conf << "\t$(MAKE) -f $(ZSRC)/win32/Makefile.#{$nmake ? 'msc' : 'gcc'} TOP=$(ZSRC) $@\n"
         conf << "install-so: $(topdir)/#{dll}"
         conf << "$(topdir)/#{dll}: $(ZIMPLIB)\n"
-        conf << "\t$(Q) $(COPY) #{dll} $(BINDIR)\n"
+        conf << "\t$(Q) $(COPY) #{dll} $(@D)\n"
       end
     end
     conf