diff --git a/CMakeLists.txt b/CMakeLists.txt
index 4fc7508c3..fbfa0bd25 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -147,7 +147,7 @@ if(UNIX
   if(M_LIBRARY)
     set(M_LIBRARY m)
   else()
-    set(M_LIBRARY)
+    set(M_LIBRARY "")
   endif()
 else()
   # libm is not available or not needed.