diff --git a/doc/CMakeLists.txt b/doc/CMakeLists.txt
index ba3d75e90..8d4692fdb 100644
--- a/doc/CMakeLists.txt
+++ b/doc/CMakeLists.txt
@@ -8,7 +8,8 @@ option(GTSAM_GENERATE_DOC_XML            "Enable/Disable doxygen XML output"
 
 # add a target to generate API documentation with Doxygen
 if (GTSAM_BUILD_DOCS)
-    # Convert configuration to YES/NO variables
+    # The following if statements convert ON/OFF CMake flags to YES/NO variables
+    # since Doxygen expects YES/NO for boolean options.
     if (GTSAM_BUILD_DOC_HTML)
         set(GTSAM_BUILD_DOC_HTML_YN "YES")
     else()