--- a/build/moz.configure/util.configure
+++ b/build/moz.configure/util.configure
@@ -59,16 +59,42 @@ def is_absolute_or_relative(path):
 
 @imports(_import='mozpack.path', _as='mozpath')
 def normsep(path):
     return mozpath.normsep(path)
 
 
 @imports('ctypes')
 @imports(_from='ctypes', _import='wintypes')
+@imports(_from='mozbuild.configure.constants', _import='WindowsBinaryType')
+def windows_binary_type(path):
+    """Obtain the type of a binary on Windows.
+
+    Returns WindowsBinaryType constant.
+    """
+    GetBinaryTypeW = ctypes.windll.kernel32.GetBinaryTypeW
+    GetBinaryTypeW.argtypes = [wintypes.LPWSTR, wintypes.POINTER(wintypes.DWORD)]
+    GetBinaryTypeW.restype = wintypes.BOOL
+
+    bin_type = wintypes.DWORD()
+    res = GetBinaryTypeW(path, ctypes.byref(bin_type))
+    if not res:
+        die('could not obtain binary type of %s' % path)
+
+    if bin_type.value == 0:
+        return WindowsBinaryType('win32')
+    elif bin_type.value == 6:
+        return WindowsBinaryType('win64')
+    # If we see another binary type, something is likely horribly wrong.
+    else:
+        die('unsupported binary type on %s: %s' % (path, bin_type))
+
+
+@imports('ctypes')
+@imports(_from='ctypes', _import='wintypes')
 def get_GetShortPathNameW():
     GetShortPathNameW = ctypes.windll.kernel32.GetShortPathNameW
     GetShortPathNameW.argtypes = [wintypes.LPCWSTR, wintypes.LPWSTR,
                                   wintypes.DWORD]
     GetShortPathNameW.restype = wintypes.DWORD
     return GetShortPathNameW
 
 

--- a/moz.configure
+++ b/moz.configure
@@ -290,12 +290,22 @@ def nsis_version(nsis):
 
     if ver < nsis_min_version:
         raise FatalCheckError('To build the installer you must have NSIS'
                               ' version %s or greater in your path'
                               % nsis_min_version)
 
     return ver
 
+# And that makensis is 32-bit.
+@depends_if(nsis)
+@checking('for 32-bit NSIS')
+def nsis_binary_type(nsis):
+    bin_type = windows_binary_type(nsis)
+    if bin_type != 'win32':
+        raise FatalCheckError('%s is not a 32-bit Windows application' % nsis)
+
+    return 'yes'
+
 
 # Fallthrough to autoconf-based configure
 include('build/moz.configure/old.configure')
 # Please do not add anything after the include of old.configure.

--- a/python/mozbuild/mozbuild/configure/constants.py
+++ b/python/mozbuild/mozbuild/configure/constants.py
@@ -58,16 +58,21 @@ CPU_bitness = {
 
 CPU = EnumString.subclass(*CPU_bitness.keys())
 
 Endianness = EnumString.subclass(
     'big',
     'little',
 )
 
+WindowsBinaryType = EnumString.subclass(
+    'win32',
+    'win64',
+)
+
 # The order of those checks matter
 CPU_preprocessor_checks = OrderedDict((
     ('x86', '__i386__ || _M_IX86'),
     ('x86_64', '__x86_64__ || _M_X64'),
     ('arm', '__arm__ || _M_ARM'),
     ('aarch64', '__aarch64__'),
     ('ia64', '__ia64__'),
     ('s390x', '__s390x__'),