--- a/phonon/CMakeLists.txt
+++ b/phonon/CMakeLists.txt
@@ -78,7 +78,7 @@ if (PHONON_NO_PLATFORMPLUGIN)
     add_definitions(-DQT_NO_PHONON_PLATFORMPLUGIN)
 endif (PHONON_NO_PLATFORMPLUGIN)
 
-add_definitions(-DPHONON_LIBRARY_PATH="${PLUGIN_INSTALL_DIR}/plugins")
+add_definitions(-DPHONON_LIBRARY_PATH="${CMAKE_INSTALL_PREFIX}/${PLUGIN_INSTALL_DIR}/plugins")
 
 automoc4_add_library(phonon SHARED ${phonon_LIB_SRCS})
 target_link_libraries(phonon ${QT_QTCORE_LIBRARY} ${QT_QTGUI_LIBRARY})