diff --git a/glib/valgrind.h b/glib/valgrind.h
index 5aed0dfca..30ccceb0a 100644
--- a/glib/valgrind.h
+++ b/glib/valgrind.h
@@ -130,11 +130,11 @@
 #  define PLAT_x86_darwin 1
 #elif defined(__APPLE__) && defined(__x86_64__)
 #  define PLAT_amd64_darwin 1
-#elif (defined(__MINGW32__) && !defined(__MINGW64__)) \
+#elif (defined(__MINGW32__) && defined(__i386__)) \
       || defined(__CYGWIN32__) \
       || (defined(_WIN32) && defined(_M_IX86))
 #  define PLAT_x86_win32 1
-#elif defined(__MINGW64__) \
+#elif (defined(__MINGW64__) && defined(__x86_64__)) \
       || (defined(_WIN64) && defined(_M_X64))
 #  define PLAT_amd64_win64 1
 #elif defined(__linux__) && defined(__i386__)