diff --git a/CMakeLists.txt b/CMakeLists.txt
index 2d3097c0d..824624db0 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -3,7 +3,7 @@ project(POLARSSL C)
 
 enable_testing()
 
-string(REGEX MATCH "clang" CMAKE_COMPILER_IS_CLANG "${CMAKE_C_COMPILER}")
+string(REGEX MATCH "Clang" CMAKE_COMPILER_IS_CLANG "${CMAKE_C_COMPILER_ID}")
 
 if(CMAKE_COMPILER_IS_GNUCC)
   set(CMAKE_C_FLAGS "${CMAKE_C_FLAGS} -Wall -Wextra -W -Wdeclaration-after-statement")