diff --git a/tests/CMakeLists.txt b/tests/CMakeLists.txt
index 651e778..c757a11 100644
--- a/tests/CMakeLists.txt
+++ b/tests/CMakeLists.txt
@@ -327,3 +327,17 @@ foreach(_t IN LISTS _eboot_test_targets)
     endif()
 endforeach()
 
+# --- printf format guard ---
+#
+# A format warning in a unit-test program is an error: test_boot_log once
+# printed "11/<garbage> tests passed" behind a warning nobody acted on.
+# Applies to the unit-test programs in this directory (and the sources they
+# compile directly); the libraries, firmware and tests/fuzz are unchanged.
+if(CMAKE_C_COMPILER_ID MATCHES "GNU|Clang")
+    foreach(_t IN LISTS _eboot_test_targets)
+        get_target_property(_type ${_t} TYPE)
+        if(_type STREQUAL "EXECUTABLE")
+            target_compile_options(${_t} PRIVATE -Werror=format)
+        endif()
+    endforeach()
+endif()
diff --git a/tests/unit/test_boot_log.c b/tests/unit/test_boot_log.c
index 0bde90f..c2207b8 100644
--- a/tests/unit/test_boot_log.c
+++ b/tests/unit/test_boot_log.c
@@ -18,6 +18,7 @@
 #include <string.h>
 #include <stdlib.h>
 
+static int tests_run = 0;
 static int tests_passed = 0;
 
 #define ASSERT(condition)                                                     \
@@ -32,6 +33,7 @@ static int tests_passed = 0;
 #define RUN(test)                                                             \
     do {                                                                      \
         reset_fixture();                                                      \
+        tests_run++;                                                          \
         test();                                                               \
         tests_passed++;                                                       \
         printf("[PASS] %s\n", #test);                                         \
@@ -300,6 +302,6 @@ int main(void)
     RUN(test_clear_reports_erase_failure);
     RUN(test_append_does_not_advance_head_when_write_fails);
     RUN(test_entry_layout_is_stable);
-    printf("\n%d/%d tests passed\n", tests_passed);
+    printf("\n%d/%d tests passed\n", tests_passed, tests_run);
     return 0;
 }