diff --git a/src/CMakeLists.txt b/src/CMakeLists.txt
index 6bf4ff0d..31f0556d 100644
--- a/src/CMakeLists.txt
+++ b/src/CMakeLists.txt
@@ -79,7 +79,7 @@ endif()
 
 # Make GCC and Clang warn about declarations that VS 2010 and 2012 won't accept
 # for all source files that VS will build
-if (${CMAKE_C_COMPILER_ID} STREQUAL GNU OR ${CMAKE_C_COMPILER_ID} STREQUAL Clang)
+if ("${CMAKE_C_COMPILER_ID}" STREQUAL "GNU" OR "${CMAKE_C_COMPILER_ID}" STREQUAL "Clang")
     if (WIN32)
         set(windows_SOURCES ${glfw_SOURCES})
     else()