diff --git a/CMakeLists.txt b/CMakeLists.txt
index 7656fc0b..cbfe6953 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -9,7 +9,13 @@ include(cmake/code-coverage.cmake)
 enable_testing()
 # activate code coverage for all executables + libraries (when -DCODE_COVERAGE=ON ??)
 add_code_coverage()
-add_code_coverage_all_targets()
+
+# 1. assuming that /nix/store/ prefixes .hpp files belonging to gcc, catch2 etc.
+#    we're not interested in code coverage for these sources.
+# 2. exclude the utest/ subdir, we don't need coverage on the unit tests themselves;
+#    rather,  want coverage on the code that the unit tests exercise.
+#
+add_code_coverage_all_targets(EXCLUDE /nix/store/* utest/*)
 
 # always write compile_commands.json
 set(CMAKE_EXPORT_COMPILE_COMMANDS ON CACHE INTERNAL "")
diff --git a/img/lcov1.png b/img/lcov1.png
index c8e66e11..4fb14106 100755
Binary files a/img/lcov1.png and b/img/lcov1.png differ