diff --git a/doc/CMakeLists.txt b/doc/CMakeLists.txt
index 17541786a..dbd1991a7 100644
--- a/doc/CMakeLists.txt
+++ b/doc/CMakeLists.txt
@@ -3,8 +3,8 @@ find_package(Doxygen)
 if(Doxygen_FOUND)
     configure_file(${CMAKE_CURRENT_SOURCE_DIR}/Doxyfile.in ${CMAKE_CURRENT_BINARY_DIR}/Doxyfile @ONLY)
     add_custom_target(doc ${DOXYGEN_EXECUTABLE} ${CMAKE_CURRENT_BINARY_DIR}/Doxyfile
-	    WORKING_DIRECTORY ${CMAKE_CURRENT_SOURCE_DIR}/..
-	    COMMENT "Generating API documentation with Doxygen"
-	    VERBATIM
+      WORKING_DIRECTORY ${CMAKE_CURRENT_SOURCE_DIR}/..
+      COMMENT "Generating API documentation with Doxygen"
+      VERBATIM
     )
 endif()