diff --git a/libs/pbd/wscript b/libs/pbd/wscript
index eff38d7b8b..a89edac002 100644
--- a/libs/pbd/wscript
+++ b/libs/pbd/wscript
@@ -145,11 +145,7 @@ def build(bld):
     if bld.env['build_target'] == 'x86_64':
         obj.defines += [ 'USE_X86_64_ASM' ]
     if bld.env['build_target'] == 'mingw':
-        import re
-        import platform as PLATFORM
-        u = PLATFORM.uname ()
-        cpu = u[4]
-        if re.search ("(x86_64|AMD64)", cpu) != None:
+        if re.search ('/^x86_64/', str(bld.env['CC'])):
             obj.defines += [ 'USE_X86_64_ASM' ]
             obj.defines += ['NO_POSIX_MEMALIGN' ]
         obj.source += [ 'windows_special_dirs.cc' ]