diff --git a/CMakeLists.txt b/CMakeLists.txt
index 915a347..ddcd3ba 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -95,7 +95,9 @@ set(GR_INCLUDE_DIR      include)
 set(GR_DATA_DIR         share)
 set(GR_PKG_DATA_DIR     ${GR_DATA_DIR}/${CMAKE_PROJECT_NAME})
 set(GR_DOC_DIR          ${GR_DATA_DIR}/doc)
-set(GR_PKG_DOC_DIR      ${GR_DOC_DIR}/${CMAKE_PROJECT_NAME})
+if (NOT GR_PKG_DOC_DIR)
+    set(GR_PKG_DOC_DIR      ${GR_DOC_DIR}/${CMAKE_PROJECT_NAME})
+endif()
 set(GR_CONF_DIR         etc)
 set(GR_PKG_CONF_DIR     ${GR_CONF_DIR}/${CMAKE_PROJECT_NAME}/conf.d)
 set(GR_LIBEXEC_DIR      libexec)