diff -r 210bb28ca4fb -r ee2e4a2c3690 setup.py
--- a/setup.py	Wed Apr 27 09:23:39 2016 -0700
+++ b/setup.py	Thu Apr 28 08:52:13 2016 -0700
@@ -57,6 +57,7 @@
 
 ispypy = "PyPy" in sys.version
 
+import ctypes
 import os, stat, subprocess, time
 import re
 import shutil
@@ -369,8 +370,34 @@
         if isinstance(self.compiler, HackedMingw32CCompiler):
             self.compiler.compiler_so = self.compiler.compiler # no -mdll
             self.compiler.dll_libraries = [] # no -lmsrvc90
-        hv = sys.hexversion
-        pythonlib = 'python%d%d' % (hv >> 24, (hv >> 16) & 0xff)
+
+        # Different Python installs can have different Python library
+        # names. e.g. the official CPython distribution uses pythonXY.dll
+        # and MinGW uses libpythonX.Y.dll.
+        _kernel32 = ctypes.windll.kernel32
+        _kernel32.GetModuleFileNameA.argtypes = [ctypes.c_void_p,
+                                                 ctypes.c_void_p,
+                                                 ctypes.c_ulong]
+        _kernel32.GetModuleFileNameA.restype = ctypes.c_ulong
+        size = 1000
+        buf = ctypes.create_string_buffer(size + 1)
+        filelen = _kernel32.GetModuleFileNameA(sys.dllhandle, ctypes.byref(buf),
+                                               size)
+
+        if filelen > 0 and filelen != size:
+            dllbasename = os.path.basename(buf.value)
+            if not dllbasename.lower().endswith('.dll'):
+                raise SystemExit('Python DLL does not end with .dll: %s' %
+                                 dllbasename)
+            pythonlib = dllbasename[:-4]
+        else:
+            log.warn('could not determine Python DLL filename; '
+                     'assuming pythonXY')
+
+            hv = sys.hexversion
+            pythonlib = 'python%d%d' % (hv >> 24, (hv >> 16) & 0xff)
+
+        log.info('using %s as Python library name' % pythonlib)
         with open('mercurial/hgpythonlib.h', 'wb') as f:
             f.write('/* this file is autogenerated by setup.py */\n')
             f.write('#define HGPYTHONLIB "%s"\n' % pythonlib)