--- dev-libs/boost/boost-1.55.0-r2.ebuild	2014-08-14 11:01:06.000000000 +0200
+++ dev-libs/boost/boost-1.55.0-r2.ebuild	2014-09-02 10:49:17.387277877 +0200
@@ -159,7 +159,14 @@
 	OPTIONS+=" --layout=system"
 	OPTIONS+=" threading=$(usex threads multi single) link=$(usex static-libs shared,static shared)"
 
-	[[ ${CHOST} == *-winnt* ]] && OPTIONS+=" -sNO_BZIP2=1"
+	if [[ ${CHOST} == *-winnt* ]] || [[ ${CHOST} == *-mingw* ]]; then
+		OPTIONS+=" -sNO_BZIP2=1"
+		OPTIONS+=" target-os=windows"
+		if use threads; then
+			# TODO: pthreads can still be available under Windows
+			OPTIONS+=" threadapi=win32"
+		fi
+	fi
 }
 
 multilib_src_compile() {