--- dev-libs/boost/boost-1.56.0-r1.ebuild	2015-03-03 07:31:06.000000000 +0100
+++ dev-libs/boost/boost-1.56.0-r1.ebuild	2015-03-26 12:13:09.624883805 +0100
@@ -170,7 +170,14 @@
 	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() {