diff --git a/celrs/CMakeLists.txt b/celrs/CMakeLists.txt
index 4ba593f..132cccf 100644
--- a/celrs/CMakeLists.txt
+++ b/celrs/CMakeLists.txt
@@ -2,14 +2,21 @@ add_library(celrs_crsf STATIC crsf.c)
 target_include_directories(celrs_crsf PUBLIC "${CMAKE_SOURCE_DIR}")
 target_compile_features(celrs_crsf PRIVATE c_std_23)
 
+# Platform-agnostic serial logic — calls cel_serial_platform_*();
+# symbol resolved by celrs_serial_platform (or a mock in tests)
 add_library(celrs_serial STATIC serial.c)
 target_include_directories(celrs_serial PUBLIC "${CMAKE_SOURCE_DIR}")
 target_compile_features(celrs_serial PRIVATE c_std_23)
+
+# Real platform backend — linked into production binaries only
+add_library(celrs_serial_platform STATIC)
+target_include_directories(celrs_serial_platform PUBLIC "${CMAKE_SOURCE_DIR}")
+target_compile_features(celrs_serial_platform PRIVATE c_std_23)
 if (IS_WINDOWS)
-    target_sources(celrs_serial PRIVATE platform/serial_win.c)
-    target_link_libraries(celrs_serial PRIVATE advapi32)
+    target_sources(celrs_serial_platform PRIVATE platform/serial_win.c)
+    target_link_libraries(celrs_serial_platform PRIVATE advapi32)
 elseif(IS_LINUX OR IS_MACOS)
-    target_sources(celrs_serial PRIVATE platform/serial_posix.c)
+    target_sources(celrs_serial_platform PRIVATE platform/serial_posix.c)
 endif()
 
 # Level-filtering logger — calls log_write(); symbol resolved by the final binary
diff --git a/tests/CMakeLists.txt b/tests/CMakeLists.txt
index 818aa23..dd188fb 100644
--- a/tests/CMakeLists.txt
+++ b/tests/CMakeLists.txt
@@ -38,12 +38,12 @@ target_compile_features(test_crsf PRIVATE c_std_23)
 add_test(NAME test_crsf COMMAND test_crsf)
 list(APPEND TEST_TARGETS test_crsf)
 
-# Serial tests — mocks log_write.h for any logging calls
+# Serial tests — mocks the platform backend (serial_internal.h)
 add_executable(test_serial test_serial.c)
 target_include_directories(test_serial PRIVATE "${CMAKE_SOURCE_DIR}")
 target_link_libraries(test_serial PRIVATE celrs_serial Unity::Unity CMock::CMock)
 target_compile_features(test_serial PRIVATE c_std_23)
-cmock_generate_mock(test_serial "${CMAKE_SOURCE_DIR}/celrs/log_write.h")
+cmock_generate_mock(test_serial "${CMAKE_SOURCE_DIR}/celrs/platform/serial_internal.h")
 add_test(NAME test_serial COMMAND test_serial)
 list(APPEND TEST_TARGETS test_serial)
 
diff --git a/tests/test_serial.c b/tests/test_serial.c
index d8697e0..b86a181 100644
--- a/tests/test_serial.c
+++ b/tests/test_serial.c
@@ -2,10 +2,10 @@
 
 #include "unity.h"
 #include "celrs/serial.h"
-#include "Mocklog_write.h"
+#include "Mockserial_internal.h"
 
-void setUp(void)    { Mocklog_write_Init(); }
-void tearDown(void) { Mocklog_write_Verify(); Mocklog_write_Destroy(); }
+void setUp(void)    { Mockserial_internal_Init(); }
+void tearDown(void) { Mockserial_internal_Verify(); Mockserial_internal_Destroy(); }
 
 void test_open_valid_path(void) {
     cel_serial_port* port = cel_serial_open("COM3", 400000);
@@ -64,19 +64,18 @@ void test_list_ports_null_out(void) {
     TEST_ASSERT_EQUAL_INT(-1, cel_serial_list_ports(NULL, 16));
 }
 
-void test_list_ports_runs_without_crash(void) {
+void test_list_ports_passes_max_ports_through(void) {
     char** ports = NULL;
+    cel_serial_platform_list_ports_ExpectAndReturn(&ports, 16, 2);
     int count = cel_serial_list_ports(&ports, 16);
-    /* count >= 0 is valid (may be 0 if no ports available) */
-    TEST_ASSERT_GREATER_OR_EQUAL_INT(0, count);
-    cel_serial_free_ports(ports, count);
+    TEST_ASSERT_EQUAL_INT(2, count);
 }
 
 void test_list_ports_zero_max_uses_default(void) {
     char** ports = NULL;
+    cel_serial_platform_list_ports_ExpectAndReturn(&ports, 64, 0);
     int count = cel_serial_list_ports(&ports, 0);
-    TEST_ASSERT_GREATER_OR_EQUAL_INT(0, count);
-    cel_serial_free_ports(ports, count);
+    TEST_ASSERT_EQUAL_INT(0, count);
 }
 
 void test_free_ports_null(void) {
@@ -99,7 +98,7 @@ int main(void) {
     RUN_TEST(test_flush_no_crash);
     RUN_TEST(test_flush_null);
     RUN_TEST(test_list_ports_null_out);
-    RUN_TEST(test_list_ports_runs_without_crash);
+    RUN_TEST(test_list_ports_passes_max_ports_through);
     RUN_TEST(test_list_ports_zero_max_uses_default);
     RUN_TEST(test_free_ports_null);
     RUN_TEST(test_free_ports_zero_count);
diff --git a/tools/CMakeLists.txt b/tools/CMakeLists.txt
index 3816220..7b65043 100644
--- a/tools/CMakeLists.txt
+++ b/tools/CMakeLists.txt
@@ -1,4 +1,4 @@
 add_executable(telemetry telemetry.c)
 target_include_directories(telemetry PRIVATE "${CMAKE_SOURCE_DIR}")
 target_compile_features(telemetry PRIVATE c_std_23)
-target_link_libraries(telemetry PRIVATE celrs_crsf celrs_serial celrs_logger celrs_log_write)
+target_link_libraries(telemetry PRIVATE celrs_crsf celrs_serial celrs_serial_platform celrs_logger celrs_log_write)