diff --git a/m4/ax_am_jobserver.m4 b/m4/ax_am_jobserver.m4
index dfbcdbb2f..7da8d5e71 100644
--- a/m4/ax_am_jobserver.m4
+++ b/m4/ax_am_jobserver.m4
@@ -33,7 +33,9 @@
 #   and this notice are preserved. This file is offered as-is, without any
 #   warranty.
 
-#serial 8
+#serial 8.1
+# Local update: Make the increment of enable-jobserver so it isn't executable
+# and is more posix syntax.
 
 AC_DEFUN([AX_AM_JOBSERVER], [
     AC_REQUIRE([AX_COUNT_CPUS])
@@ -45,7 +47,7 @@ AC_DEFUN([AX_AM_JOBSERVER], [
     ],, [enable_jobserver=m4_ifval([$1],[$1],[yes])])
     if test "x$enable_jobserver" = "xyes"; then
         enable_jobserver=$CPU_COUNT
-        ((enable_jobserver++))
+        : $((enable_jobserver+=1))
     fi
     m4_pattern_allow(AM_MAKEFLAGS)
     if test "x$enable_jobserver" != "xno"; then