diff --git a/setup.py b/setup.py
index 4599927a585..58f7e8c2390 100644
--- a/setup.py
+++ b/setup.py
@@ -433,7 +433,8 @@ class PyBuildExt(build_ext):
         # _json speedups
         exts.append( Extension("_json", ["_json.c"]) )
         # Python C API test module
-        exts.append( Extension('_testcapi', ['_testcapimodule.c']) )
+        exts.append( Extension('_testcapi', ['_testcapimodule.c'],
+                               depends=['testcapi_long.h']) )
         # profiler (_lsprof is for cProfile.py)
         exts.append( Extension('_lsprof', ['_lsprof.c', 'rotatingtree.c']) )
         # static Unicode character database