diff --git a/src/os/CMakeLists.txt b/src/os/CMakeLists.txt
index cb64db5..1eecf48 100644
--- a/src/os/CMakeLists.txt
+++ b/src/os/CMakeLists.txt
@@ -78,8 +78,9 @@ elseif(UNIX)
   check_library_exists(c clock_gettime "" HAVE_CLOCK_GETTIME)
   if(NOT HAVE_CLOCK_GETTIME)
     # Before glibc 2.17, clock_gettime was in librt.
-    check_library_exists(rt clock_gettime "time.h" HAVE_CLOCK_GETTIME)
-    if(HAVE_CLOCK_GETTIME)
+    check_library_exists(rt clock_gettime "time.h" HAVE_CLOCK_GETTIME_RT)
+    if(HAVE_CLOCK_GETTIME_RT)
+      set(HAVE_CLOCK_GETTIME "${HAVE_CLOCK_GETTIME_RT}")
       target_link_libraries(OSAPI INTERFACE rt)
     endif()
   endif()