diff --git a/build/configure.ac.system b/build/configure.ac.system
index 564d66d1e..b405740da 100644
--- a/build/configure.ac.system
+++ b/build/configure.ac.system
@@ -113,7 +113,7 @@ AC_CHECK_HEADER(fenv.h,
 
 dnl check for misc headers and functions
 AC_CHECK_HEADERS([libgen.h byteswap.h signal.h setjmp.h fenv.h])
-AC_CHECK_FUNCS([vasnprintf link ctime_r drand48 flockfile ffs])
+AC_CHECK_FUNCS([vasnprintf link ctime_r drand48 flockfile funlockfile ffs])
 
 dnl check for win32 headers (this detects mingw as well)
 AC_CHECK_HEADERS([windows.h], have_windows=yes, have_windows=no)