diff --git a/CMakeLists.txt b/CMakeLists.txt
index 5f3a64a8..36f48769 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -492,7 +492,7 @@ execute_process(
 if(CACHELINE_SIZE STREQUAL ""
    OR CACHELINE_SIZE EQUAL 0
    OR CACHELINE_SIZE EQUAL -1
-   OR CACHELINE_SIZE EQUAL "undefined")
+   OR CACHELINE_SIZE STREQUAL "undefined")
   set(ZMQ_CACHELINE_SIZE 64)
 else()
   set(ZMQ_CACHELINE_SIZE ${CACHELINE_SIZE})