diff --git a/.gitea/workflows/ci.yaml b/.gitea/workflows/ci.yaml
index d46f8f8..7113c07 100644
--- a/.gitea/workflows/ci.yaml
+++ b/.gitea/workflows/ci.yaml
@@ -67,34 +67,6 @@ jobs:
           fail_on_failure: 'false'
       - run: echo "🍏 This job's status is ${{ job.status }}."
 
-  thread_sanitizer:
-    runs-on: ubuntu-latest
-    steps:
-      - name: Check out repository code
-        uses: actions/checkout@v4
-      - name: dependencies
-        run: |
-          sudo apt-get update -y
-          sudo apt-get install -y cmake gcc moreutils
-      # The thread tests assert exclusive ownership of pool slots and reserved
-      # ranges, which is checkable without tooling and runs in the job above.
-      # This is the run that proves there is no data race underneath them.
-      # libtsan arrives with gcc (libgcc-N-dev depends on it); the script
-      # disables ASLR because TSan aborts on kernels with vm.mmap_rnd_bits > 28.
-      - name: thread sanitizer
-        run: |
-          scripts/thread_test.sh build/tsan --output-junit "$(pwd)/tsan-junit.xml"
-      - name: publish thread sanitizer results
-        if: always()
-        uses: mikepenz/action-junit-report@v4
-        with:
-          report_paths: 'tsan-junit.xml'
-          annotate_only: true
-          detailed_summary: true
-          include_passed: true
-          fail_on_failure: 'true'
-      - run: echo "🍏 This job's status is ${{ job.status }}."
-
   mutation_test:
     runs-on: ubuntu-latest
     steps:
diff --git a/CMakeLists.txt b/CMakeLists.txt
index 69dbe30..4ea8499 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -107,6 +107,19 @@ if(AKERR_SANITIZE AND NOT CMAKE_C_COMPILER_ID MATCHES "GNU|Clang")
         "AKERR_SANITIZE requires GCC or Clang, not ${CMAKE_C_COMPILER_ID}")
 endif()
 
+if(AKERR_SANITIZE STREQUAL "thread" AND CMAKE_SYSTEM_NAME STREQUAL "Linux")
+    # ThreadSanitizer reserves a fixed, very large virtual-address range. Linux
+    # ASLR can put a loader mapping inside it before the runtime starts, which
+    # makes every test fail with "unexpected memory mapping" before main().
+    # Run the instrumented tests under the normal util-linux ASLR wrapper.
+    find_program(AKERR_SETARCH_EXECUTABLE setarch)
+    if(NOT AKERR_SETARCH_EXECUTABLE)
+        message(FATAL_ERROR
+            "AKERR_SANITIZE=thread on Linux requires setarch (util-linux) to "
+            "start tests with ASLR disabled.")
+    endif()
+endif()
+
 function(akerr_instrument_for_sanitizers _target)
     if(AKERR_SANITIZE)
         target_compile_options(${_target} PRIVATE
@@ -252,7 +265,13 @@ foreach(_test IN LISTS AKERR_TESTS)
         target_link_libraries(test_${_test} PRIVATE Threads::Threads)
     endif()
     akerr_instrument_for_sanitizers(test_${_test})
-    add_test(NAME ${_test} COMMAND test_${_test})
+    if(AKERR_SANITIZE STREQUAL "thread" AND CMAKE_SYSTEM_NAME STREQUAL "Linux")
+        add_test(NAME ${_test}
+                 COMMAND ${AKERR_SETARCH_EXECUTABLE} ${CMAKE_SYSTEM_PROCESSOR}
+                         -R $<TARGET_FILE:test_${_test}>)
+    else()
+        add_test(NAME ${_test} COMMAND test_${_test})
+    endif()
     # A sanitizer report is a test failure. Without halt_on_error the runtime
     # prints and continues, which leaves a race to be noticed in the log by
     # somebody reading it -- and under a race storm the reporting itself is slow
@@ -263,6 +282,14 @@ foreach(_test IN LISTS AKERR_TESTS)
     endif()
 endforeach()
 
+# HANDLE_GROUP deliberately enters the next case label. Keep that public macro
+# compiling with the warning enabled, so a future macro edit cannot restore the
+# warning for consumers which adopt -Wextra.
+if(CMAKE_C_COMPILER_ID MATCHES "GNU|Clang")
+    target_compile_options(test_err_handle_group PRIVATE
+                           -Werror=implicit-fallthrough)
+endif()
+
 set_tests_properties(
     ${AKERR_WILL_FAIL_TESTS}
     PROPERTIES WILL_FAIL TRUE
diff --git a/include/akerror.tmpl.h b/include/akerror.tmpl.h
index dad4c45..ede8fcc 100644
--- a/include/akerror.tmpl.h
+++ b/include/akerror.tmpl.h
@@ -391,6 +391,18 @@ akerr_ErrorContext AKERR_NOIGNORE *__akerr_copy_string(char *destination, int ca
  * Defines for the ATTEMPT/CATCH/CLEANUP/PROCESS/HANDLE/FINISH process
  */
 
+/*
+ * HANDLE_GROUP deliberately enters the next case label. GCC and clang both
+ * understand this spelling in the C modes supported by libakerror. Other
+ * compilers keep the established control flow without receiving an attribute
+ * they do not implement.
+ */
+#if defined(__GNUC__) || defined(__clang__)
+#define AKERR_FALLTHROUGH __attribute__((fallthrough));
+#else
+#define AKERR_FALLTHROUGH
+#endif
+
 #define ATTEMPT					\
     switch ( 0 ) {				\
     case 0:					\
@@ -443,6 +455,7 @@ akerr_ErrorContext AKERR_NOIGNORE *__akerr_copy_string(char *destination, int ca
     __err_context->handled = true;
 
 #define HANDLE_GROUP(__err_context, __err_status)			\
+    AKERR_FALLTHROUGH					\
     case __err_status:							\
     __err_context->stacktracebufptr = (char *)&__err_context->stacktracebuf; \
     __err_context->handled = true;