diff --git a/CMakeLists.txt b/CMakeLists.txt
index b037f39..35a7ae3 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -15,7 +15,7 @@
 option(nanopb_MSVC_STATIC_RUNTIME "Link static runtime libraries" ON)
 
 find_program(nanopb_PROTOC_PATH protoc)
-if(NOT EXISTS nanopb_PROTOC_PATH)
+if(NOT EXISTS ${nanopb_PROTOC_PATH})
     message(FATAL_ERROR "protoc compiler not found")
 endif()