diff --git a/configure.ac b/configure.ac
index bf0f3f8f5..2b4bc4319 100644
--- a/configure.ac
+++ b/configure.ac
@@ -541,10 +541,17 @@ case $host in
      CPPFLAGS="$CPPFLAGS -DMAC_OSX"
      OBJCXXFLAGS="$CXXFLAGS"
      ;;
+   *android*)
+     dnl make sure android stays above linux for hosts like *linux-android*
+     LEVELDB_TARGET_FLAGS="-DOS_ANDROID"
+     ;;
    *linux*)
      TARGET_OS=linux
      LEVELDB_TARGET_FLAGS="-DOS_LINUX"
      ;;
+   *kfreebsd*)
+     LEVELDB_TARGET_FLAGS="-DOS_KFREEBSD"
+     ;;
    *freebsd*)
      LEVELDB_TARGET_FLAGS="-DOS_FREEBSD"
      ;;
@@ -554,10 +561,17 @@ case $host in
    *netbsd*)
      LEVELDB_TARGET_FLAGS="-DOS_NETBSD"
      ;;
+   *dragonfly*)
+     LEVELDB_TARGET_FLAGS="-DOS_DRAGONFLYBSD"
+     ;;
+   *solaris*)
+     LEVELDB_TARGET_FLAGS="-DOS_SOLARIS"
+     ;;
+   *hpux*)
+     LEVELDB_TARGET_FLAGS="-DOS_HPUX"
+     ;;
    *)
-     OTHER_OS=`echo ${host_os} | awk '{print toupper($0)}'`
-     AC_MSG_WARN([Guessing LevelDB OS as OS_${OTHER_OS}, please check whether this is correct, if not add an entry to configure.ac.])
-     LEVELDB_TARGET_FLAGS="-DOS_${OTHER_OS}"
+     AC_MSG_ERROR(Cannot build leveldb for $host. Please file a bug report.)
      ;;
 esac