diff --git a/sources.cmake b/sources.cmake
--- a/sources.cmake
+++ b/sources.cmake
@@ -171,4 +171,8 @@
 tommath_cutoffs.h
 tommath_private.h
 tommath_superclass.h
 )
+
+if(WIN32)
+    list(APPEND SOURCES tommath.def)
+endif()