diff --git a/src/CMakeLists.txt b/src/CMakeLists.txt
index 03e1f9a2..cf9720b3 100644
--- a/src/CMakeLists.txt
+++ b/src/CMakeLists.txt
@@ -43,7 +43,7 @@ if(UNIX)
 
   if(${CMAKE_SYSTEM_NAME} STREQUAL "Linux")
     add_definitions(-DUNIX_LINUX)
-    if($ENV{USE_MUSL} STREQUAL "YES")
+    if("$ENV{USE_MUSL}" STREQUAL "YES")
       add_definitions(-DUNIX_LINUX_MUSL)
     endif()
   endif()