diff --git a/tools/hdltool_readme.txt b/tools/hdltool_readme.txt
index e2553faf0fb6e1cbf707fe699540f16db70a3c54..39d2c09d5fe86a91f769ee93c566c47a916039a2 100644
--- a/tools/hdltool_readme.txt
+++ b/tools/hdltool_readme.txt
@@ -277,6 +277,11 @@ d) hdllib.cfg key descriptions
     Global root path (e.g. $HDL_BUILD_DIR) or local library path (e.g. '') to the build directory for simulation. The path gets extended with the
     tool_name_synth from hdltool.cfg.
 
+- modelsim_search_libraries =
+    List of IP technology search libraries that will be put in the -L {} option of a Modelsim simulation configuration in the mpf. This avoids that all
+    IP technology needs to be compiled into the work library. The -L {} option is needed for simulations in libraries that use generated IP like
+    ip_stratixiv_phy_xaui which do not recognize the IP technology libraries mapping in [libraries] section in the mpf.
+
 - modelsim_copy_files =
     Copy listed all directories and files for simulation with Modelsim, used when tool_name_sim = modelsim in hdltool.cfg.