diff --git a/acinclude.m4 b/acinclude.m4
index 3c58fb055..169178315 100644
--- a/acinclude.m4
+++ b/acinclude.m4
@@ -37,7 +37,7 @@ AC_DEFUN([GUILE_HEADER_LIBC_WITH_UNISTD],
       [
         if test "$ac_cv_header_libc_h" = "no"; then
           guile_cv_header_libc_with_unistd="no"
-        elif test "$ac_cv_header_unistd.h" = "no"; then
+        elif test "$ac_cv_header_unistd_h" = "no"; then
           guile_cv_header_libc_with_unistd="yes"
         else
           AC_TRY_COMPILE(