Index: build/generator/gen_make.py
===================================================================
--- build/generator/gen_make.py	(revision 17814)
+++ build/generator/gen_make.py	(working copy)
@@ -148,10 +148,16 @@
       fname = '%s/swig_%s_external_runtime.swg' % (self.swig.proxy_dir, lang)
       swig_runtime_fnames.append(fname)
     if not self.release_mode:
+      # external_runtime.py generates the SWIG runtimes for all languages
+      # the first time it is called
+      first_runtime = swig_runtime_fnames[0]
+      other_runtimes = " ".join(swig_runtime_fnames[1:])
       self.ofile.write(
-        '%s:\n' % " ".join(swig_runtime_fnames) +
-        '\tcd $(top_srcdir) && $(PYTHON)' +
+        '%s: %s\n'
+        '%s:\n'
+        '\tcd $(top_srcdir) && $(PYTHON)'
         ' build/generator/swig/external_runtime.py build.conf "$(SWIG)"\n\n'
+          % (other_runtimes, first_runtime, first_runtime)
       )
 
     self.ofile.write(