diff --git a/src/CMakeLists.txt b/src/CMakeLists.txt
index 5f2c0cb1f..69dea5efb 100644
--- a/src/CMakeLists.txt
+++ b/src/CMakeLists.txt
@@ -303,6 +303,7 @@ set(SLIC3R_TEST_SOURCES
     ${TESTDIR}/libslic3r/test_fill.cpp
     ${TESTDIR}/libslic3r/test_flow.cpp
     ${TESTDIR}/libslic3r/test_gcodewriter.cpp
+    ${TESTDIR}/libslic3r/test_gcode.cpp
     ${TESTDIR}/libslic3r/test_geometry.cpp
     ${TESTDIR}/libslic3r/test_log.cpp
     ${TESTDIR}/libslic3r/test_model.cpp
@@ -544,6 +545,7 @@ if (SLIC3R_BUILD_TESTS)
     endif()
     configure_file("${TESTDIR}/test_options.hpp.in" "${TESTDIR}/test_options.hpp")
     add_executable(slic3r_test ${SLIC3R_TEST_SOURCES}) 
+    target_compile_options(slic3r_test PUBLIC -DSLIC3R_TEST)
     add_test(NAME TestSlic3r COMMAND slic3r_test)
     target_compile_features(slic3r_test PUBLIC cxx_std_14)
     target_include_directories(slic3r_test PUBLIC cxx_std_14 ${SLIC3R_INCLUDES})
diff --git a/xs/src/libslic3r/GCode/CoolingBuffer.cpp b/xs/src/libslic3r/GCode/CoolingBuffer.cpp
index 786a9a8e4..a9db021b8 100644
--- a/xs/src/libslic3r/GCode/CoolingBuffer.cpp
+++ b/xs/src/libslic3r/GCode/CoolingBuffer.cpp
@@ -50,7 +50,8 @@ apply_speed_factor(std::string &line, float speed_factor, float min_print_speed)
     // replace speed in string
     {
         std::ostringstream oss;
-        oss << speed;
+        oss.precision(3);
+        oss << std::fixed << speed;
         line.replace(pos+1, (last_pos-pos), oss.str());
     }
 }
diff --git a/xs/src/libslic3r/GCode/CoolingBuffer.hpp b/xs/src/libslic3r/GCode/CoolingBuffer.hpp
index c290612ba..a45a2d1b8 100644
--- a/xs/src/libslic3r/GCode/CoolingBuffer.hpp
+++ b/xs/src/libslic3r/GCode/CoolingBuffer.hpp
@@ -37,6 +37,10 @@ class CoolingBuffer {
     float                       _min_print_speed;
 };
 
+#ifdef SLIC3R_TEST
+void apply_speed_factor(std::string &line, float speed_factor, float min_print_speed);
+#endif
+
 }
 
 #endif