diff --git a/libtransmission/tr-lpd.h b/libtransmission/tr-lpd.h
index 3d546d8bd..b279ed8b0 100644
--- a/libtransmission/tr-lpd.h
+++ b/libtransmission/tr-lpd.h
@@ -20,6 +20,10 @@ OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
 THE SOFTWARE.
 */
 
+#ifndef __TRANSMISSION__
+ #error only libtransmission should #include this header.
+#endif
+
 #ifndef _TR_LPD_H
 #define _TR_LPD_H