diff --git a/CMakeLists.txt b/CMakeLists.txt
index 23b4194..d777537 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -73,6 +73,10 @@ set(NL_FW_SOURCES
   src/sys/nl_app_api.c
   third_party/cJSON/cJSON.c)
 
+# C1: deeply nested JSON must not overflow the 6 KB HTTP task stack (parse_value recurses).
+set_source_files_properties(third_party/cJSON/cJSON.c PROPERTIES
+  COMPILE_DEFINITIONS "CJSON_NESTING_LIMIT=8")
+
 set(NL_FW ninlight_${NINLIGHT_DEVICE})
 add_executable(${NL_FW} ${NL_SDK_BOOT_SOURCES} ${NL_FW_SOURCES} ${NL_SDK_OBJECTS})
 set_target_properties(${NL_FW} PROPERTIES SUFFIX ".elf")
diff --git a/test/CMakeLists.txt b/test/CMakeLists.txt
index a771b37..6b98238 100644
--- a/test/CMakeLists.txt
+++ b/test/CMakeLists.txt
@@ -15,6 +15,8 @@ enable_testing()
 # cJSON is third-party code: build it without -Werror.
 add_library(nl_cjson STATIC ${CMAKE_CURRENT_SOURCE_DIR}/../third_party/cJSON/cJSON.c)
 target_include_directories(nl_cjson PUBLIC ${CMAKE_CURRENT_SOURCE_DIR}/../third_party/cJSON)
+# C1: match the firmware's nesting limit so host tests exercise the same behaviour.
+target_compile_definitions(nl_cjson PUBLIC CJSON_NESTING_LIMIT=8)
 
 set(NL_SRC ${CMAKE_CURRENT_SOURCE_DIR}/../src)
 
diff --git a/test/test_api.c b/test/test_api.c
index 794d609..2e6fd05 100644
--- a/test/test_api.c
+++ b/test/test_api.c
@@ -100,6 +100,7 @@ static void test_post_validation(void)
     static const struct { const char *body; const char *err; } CASES[] = {
         {"not json", "invalid json"},
         {"[1,2]", "invalid json"},
+        {"{\"a\":[[[[[[[[[[[[[[[[[[[[]]]]]]]]]]]]]]]]]]]]}", "invalid json"}, /* C1: 20 levels > CJSON_NESTING_LIMIT */
         {"{\"on\":1}", "invalid on"},
         {"{\"brightness\":0}", "invalid brightness"},
         {"{\"brightness\":101}", "invalid brightness"},