diff --git a/external/CMakeLists.txt b/external/CMakeLists.txt
index ad3ae9d66..895342b1b 100644
--- a/external/CMakeLists.txt
+++ b/external/CMakeLists.txt
@@ -864,7 +864,6 @@ if(ENABLE_FEATURE_MORSEDECODER)
         CMAKE_ARGS ${COMMON_CMAKE_ARGS}
         -DGGMORSE_BUILD_TESTS=OFF
         -DGGMORSE_BUILD_EXAMPLES=OFF
-        -D_USE_MATH_DEFINES
         BUILD_BYPRODUCTS "${GGMORSE_LIBRARIES}"
         INSTALL_COMMAND ""
         TEST_COMMAND ""