diff --git a/src/lay/lay/layLibraryController.cc b/src/lay/lay/layLibraryController.cc
index 8b8639f57..df342e21f 100644
--- a/src/lay/lay/layLibraryController.cc
+++ b/src/lay/lay/layLibraryController.cc
@@ -295,7 +295,7 @@ public:
 
     LibraryController::LibFileInfo fi;
     fi.name = name;
-    fi.path = lf;
+    fi.path = tl::is_absolute (lf) ? lf : tl::combine_path (tl::absolute_path (mp_fc->lib_file), lf);
     if (! mp_fc->tech.empty ()) {
       fi.tech.insert (mp_fc->tech);
     }
@@ -315,7 +315,10 @@ public:
         } else if (k->first == technology_key) {
 
           fi.tech.clear ();
-          fi.tech.insert (k->second.to_string ());
+          std::string tn = k->second.to_string ();
+          if (! tn.empty () && tn != "*") {
+            fi.tech.insert (tn);
+          }
 
         } else if (k->first == technologies_key) {
 
@@ -375,11 +378,8 @@ do_read_lib_file (LibFileFunctionContext &fc)
 {
   tl::Eval eval;
 
-  DefineFunction define_function (&fc);
-  IncludeFunction include_function (&fc);
-
-  eval.define_function ("define", &define_function);
-  eval.define_function ("include", &include_function);
+  eval.define_function ("define", new DefineFunction (&fc));
+  eval.define_function ("include", new IncludeFunction (&fc));
   eval.set_var ("file", fc.lib_file);
   eval.set_var ("tech", fc.tech);
 
diff --git a/src/lay/lay/layLibraryController.h b/src/lay/lay/layLibraryController.h
index 6050fa198..c7970c5a4 100644
--- a/src/lay/lay/layLibraryController.h
+++ b/src/lay/lay/layLibraryController.h
@@ -51,7 +51,7 @@ class MainWindow;
  *  By making the controller a PluginDeclaration it will receive
  *  initialization and configuration calls.
  */
-class LibraryController
+class LAY_PUBLIC LibraryController
   : public lay::PluginDeclaration, public tl::Object
 {
 Q_OBJECT
@@ -116,6 +116,11 @@ public:
    */
   static LibraryController *instance ();
 
+  /**
+   *  @brief Provided for test purposes
+   */
+  static void read_lib_file (const std::string &lib_file, const std::string &tech, std::vector<LibFileInfo> &file_info);
+
 private slots:
   /**
    *  @brief Called when the file watcher detects a change in the file system
@@ -142,7 +147,6 @@ private:
 
   void sync_files ();
   void read_libs (const std::vector<LibFileInfo> &file_info, std::map<std::string, LibInfo> &new_lib_files);
-  void read_lib_file (const std::string &lib_file, const std::string &tech, std::vector<LibFileInfo> &file_info);
 };
 
 }
diff --git a/src/lay/unit_tests/layLibraryControllerTests.cc b/src/lay/unit_tests/layLibraryControllerTests.cc
new file mode 100644
index 000000000..b5785dcfa
--- /dev/null
+++ b/src/lay/unit_tests/layLibraryControllerTests.cc
@@ -0,0 +1,76 @@
+
+/*
+
+  KLayout Layout Viewer
+  Copyright (C) 2006-2026 Matthias Koefferlein
+
+  This program is free software; you can redistribute it and/or modify
+  it under the terms of the GNU General Public License as published by
+  the Free Software Foundation; either version 2 of the License, or
+  (at your option) any later version.
+
+  This program is distributed in the hope that it will be useful,
+  but WITHOUT ANY WARRANTY; without even the implied warranty of
+  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+  GNU General Public License for more details.
+
+  You should have received a copy of the GNU General Public License
+  along with this program; if not, write to the Free Software
+  Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA  02110-1301  USA
+
+*/
+
+
+#include "layLibraryController.h"
+#include "tlUnitTest.h"
+#include "tlFileUtils.h"
+
+TEST (1)
+{
+  std::string lib_file = tl::testdata () + "/lay/a.libdef";
+
+  std::vector<lay::LibraryController::LibFileInfo> file_info;
+  lay::LibraryController::read_lib_file (lib_file, "T1", file_info);
+
+  tl_assert (file_info.size () == size_t (3));
+
+  EXPECT_EQ (file_info[0].name, "");
+  EXPECT_EQ (file_info[0].path, tl::combine_path (tl::absolute_path (lib_file), "noname.gds"));
+  EXPECT_EQ (file_info[0].replicate, true);
+  EXPECT_EQ (tl::join (file_info[0].tech.begin (), file_info[0].tech.end (), ","), "T1");
+
+  EXPECT_EQ (file_info[1].name, "L2");
+  EXPECT_EQ (file_info[1].path, tl::absolute_file_path (lib_file) + ".zzz");
+  EXPECT_EQ (file_info[1].replicate, true);
+  EXPECT_EQ (file_info[1].tech.size (), size_t (0));
+
+  EXPECT_EQ (file_info[2].name, "L3");
+  EXPECT_EQ (file_info[2].path, tl::combine_path (tl::absolute_path (lib_file), "subdir/l3.gds"));
+  EXPECT_EQ (file_info[2].replicate, false);
+  EXPECT_EQ (tl::join (file_info[2].tech.begin (), file_info[2].tech.end (), ","), "T2,T3");
+}
+
+TEST(2)
+{
+  std::string lib_file = tl::testdata () + "/lay/b.libdef";
+
+  std::vector<lay::LibraryController::LibFileInfo> file_info;
+  lay::LibraryController::read_lib_file (lib_file, "TX", file_info);
+
+  tl_assert (file_info.size () == size_t (5));
+
+  EXPECT_EQ (file_info[0].name, "L0");
+  EXPECT_EQ (file_info[0].path, tl::combine_path (tl::absolute_path (lib_file), "l0.gds"));
+  EXPECT_EQ (file_info[0].replicate, true);
+  EXPECT_EQ (file_info[0].tech.size (), size_t (0));
+
+  EXPECT_EQ (file_info[1].name, "");
+  EXPECT_EQ (file_info[1].path, tl::combine_path (tl::absolute_path (lib_file), "noname.gds"));
+  EXPECT_EQ (file_info[1].replicate, true);
+  EXPECT_EQ (tl::join (file_info[1].tech.begin (), file_info[1].tech.end (), ","), "TX");
+
+  EXPECT_EQ (file_info[4].name, "L4");
+  EXPECT_EQ (file_info[4].path, tl::combine_path (tl::absolute_path (lib_file), "l4.gds"));
+  EXPECT_EQ (file_info[4].replicate, true);
+  EXPECT_EQ (tl::join (file_info[4].tech.begin (), file_info[4].tech.end (), ","), "TX");
+}
diff --git a/src/lay/unit_tests/unit_tests.pro b/src/lay/unit_tests/unit_tests.pro
index adf955966..b701fe4c1 100644
--- a/src/lay/unit_tests/unit_tests.pro
+++ b/src/lay/unit_tests/unit_tests.pro
@@ -7,6 +7,7 @@ TARGET = lay_tests
 include($$PWD/../../lib_ut.pri)
 
 SOURCES = \
+  layLibraryControllerTests.cc \
   laySalt.cc \
   layHelpIndexTest.cc \
   laySaltParsedURLTests.cc \
diff --git a/testdata/lay/a.libdef b/testdata/lay/a.libdef
new file mode 100644
index 000000000..ff4bc56af
--- /dev/null
+++ b/testdata/lay/a.libdef
@@ -0,0 +1,6 @@
+
+# A comment
+define("noname.gds");
+define("L2", file + ".zzz", technology = "");
+define("L3", "subdir/l3.gds", technologies = [ "T2", "T3" ], replicate = false);
+
diff --git a/testdata/lay/b.libdef b/testdata/lay/b.libdef
new file mode 100644
index 000000000..eadaf2604
--- /dev/null
+++ b/testdata/lay/b.libdef
@@ -0,0 +1,10 @@
+
+define("L0", "l0.gds", technology = "*");
+
+# relative to this file
+include("../lay/a.libdef");
+
+var n4 = "L4";
+var f4 = "l4.gds";
+define(n4, f4);
+