diff --git a/cmake/CMakeLists.txt b/cmake/CMakeLists.txt
index 708f0e948..826afa8f5 100644
--- a/cmake/CMakeLists.txt
+++ b/cmake/CMakeLists.txt
@@ -70,7 +70,7 @@ else()
 endif()
 
 if (UNIX AND NOT APPLE AND NOT BEOS)
-  find_library(OPENEXR_EXTRA_MATH_LIB m)
+  set(OPENEXR_EXTRA_MATH_LIB m PARENT_SCOPE)
   mark_as_advanced(OPENEXR_EXTRA_MATH_LIB)
 endif()