diff --git a/CMakeLists.txt b/CMakeLists.txt
index 19da931..20829ea 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -16,7 +16,7 @@ endif ()
 
 add_option(ENABLE_LLVM_COVERAGE "Enables the code coverage instrumentation for clang")
 if(ENABLE_LLVM_COVERAGE)
-    if (CMAKE_CXX_COMPILER_ID NOT STREQUAL "Clang")
+    if (NOT "${CMAKE_CXX_COMPILER_ID}" STREQUAL "Clang")
         message(FATAL_ERROR "ENABLE_LLVM_COVERAGE only supports the clang compiler")
     endif ()