diff --git a/tools/amalgamate.py b/tools/amalgamate.py
index d3807c6..4739a94 100755
--- a/tools/amalgamate.py
+++ b/tools/amalgamate.py
@@ -18,14 +18,14 @@
 
     self.output_c.write("// Amalgamated source file\n")
     self.output_c.write('#include "upb.h"\n')
-    self.output_c.write('#include "upb/port_def.inc"\n')
+    self.output_c.write(open("upb/port_def.inc").read())
 
     self.output_h.write("// Amalgamated source file\n")
-    self.output_h.write('#include "upb/port_def.inc"\n')
+    self.output_h.write(open("upb/port_def.inc").read())
 
   def finish(self):
-    self.output_c.write('#include "upb/port_undef.inc"\n')
-    self.output_h.write('#include "upb/port_undef.inc"\n')
+    self.output_c.write(open("upb/port_undef.inc").read())
+    self.output_h.write(open("upb/port_undef.inc").read())
 
   def _process_file(self, infile_name, outfile):
     for line in open(infile_name):