diff --git a/Modules/CMakeCCompiler.cmake.in b/Modules/CMakeCCompiler.cmake.in
index 804cce24c1..694f8b879c 100644
--- a/Modules/CMakeCCompiler.cmake.in
+++ b/Modules/CMakeCCompiler.cmake.in
@@ -26,7 +26,7 @@ if(CMAKE_COMPILER_IS_MINGW)
   set(MINGW 1)
 endif()
 set(CMAKE_C_COMPILER_ID_RUN 1)
-set(CMAKE_C_SOURCE_FILE_EXTENSIONS c)
+set(CMAKE_C_SOURCE_FILE_EXTENSIONS c;m)
 set(CMAKE_C_IGNORE_EXTENSIONS h;H;o;O;obj;OBJ;def;DEF;rc;RC)
 set(CMAKE_C_LINKER_PREFERENCE 10)
 
diff --git a/Modules/CMakeCXXCompiler.cmake.in b/Modules/CMakeCXXCompiler.cmake.in
index 35aa6c455e..c75611acff 100644
--- a/Modules/CMakeCXXCompiler.cmake.in
+++ b/Modules/CMakeCXXCompiler.cmake.in
@@ -27,7 +27,7 @@ if(CMAKE_COMPILER_IS_MINGW)
 endif()
 set(CMAKE_CXX_COMPILER_ID_RUN 1)
 set(CMAKE_CXX_IGNORE_EXTENSIONS inl;h;hpp;HPP;H;o;O;obj;OBJ;def;DEF;rc;RC)
-set(CMAKE_CXX_SOURCE_FILE_EXTENSIONS C;M;c++;cc;cpp;cxx;m;mm;CPP)
+set(CMAKE_CXX_SOURCE_FILE_EXTENSIONS C;M;c++;cc;cpp;cxx;mm;CPP)
 set(CMAKE_CXX_LINKER_PREFERENCE 30)
 set(CMAKE_CXX_LINKER_PREFERENCE_PROPAGATES 1)