diff --git a/doc/CMakeLists.txt b/doc/CMakeLists.txt
index 1d8bb75..a3a9794 100644
--- a/doc/CMakeLists.txt
+++ b/doc/CMakeLists.txt
@@ -75,11 +75,16 @@ add_custom_command(
   WORKING_DIRECTORY "${CMAKE_CURRENT_SOURCE_DIR}"
   COMMENT "Generating Doxygen-based man pages")
 
-add_custom_target(doc_doxygen true DEPENDS ${DOXYGEN_MANPAGES})
-add_dependencies(doc doc_doxygen)
+# Target to clean the files generated by Doxygen that we don't want
+# (so-called "directory references"). This cannot be done with CMake's
+# file() commands because it has to be run every time the target is
+# built, and you cannot use CMake functions in a custom target or
+# command.
+add_custom_target(clean_doxygen_garbage
+  COMMAND rm -f "${OUTPUT_DIRECTORY}/_*_owlps_libowlps*_.${SECTION}")
 
-# Clean Doxygen garbage
-file(GLOB DOXYGEN_GARBAGE "${OUTPUT_DIRECTORY}/_*_owlps_libowlps*_.${SECTION}")
-if (DOXYGEN_GARBAGE)
-  file(REMOVE ${DOXYGEN_GARBAGE})
-endif()
+# Set up the target
+add_custom_target(doc_doxygen true DEPENDS ${DOXYGEN_MANPAGES})
+
+# Add the target to the "doc" meta-target
+add_dependencies(doc doc_doxygen clean_doxygen_garbage)