diff --git a/m4/ax_platform.m4 b/m4/ax_platform.m4
index baffd1e..1747ca7 100644
--- a/m4/ax_platform.m4
+++ b/m4/ax_platform.m4
@@ -76,7 +76,7 @@
         [TARGET_LINUX="true"
         AC_DEFINE([TARGET_OS_LINUX],[1],[Whether we build for Linux])])
 
-  AM_CONDITIONAL([BUILD_WIN32],[test "x${TARGET_WINDOWS}" = "xtrue"])
+  AM_CONDITIONAL([TARGET_WIN32],[test "x${TARGET_WINDOWS}" = "xtrue"])
   AM_CONDITIONAL([TARGET_CYGWIN],[test "x${TARGET_CYGWIN}" = "xtrue"])
   AM_CONDITIONAL([TARGET_HAIKU],[test "x${TARGET_HAIKU}" = "xtrue"])
   AM_CONDITIONAL([TARGET_OSX],[test "x${TARGET_OSX}" = "xtrue"])