Index: /issm/trunk-jpl/m4/issm_options.m4
===================================================================
--- /issm/trunk-jpl/m4/issm_options.m4	(revision 25664)
+++ /issm/trunk-jpl/m4/issm_options.m4	(revision 25665)
@@ -207,12 +207,12 @@
 	dnl If macOS, check if system copy of libc has fmemopen (if it is not 
 	dnl macOS, we do not check, but still must set SYSTEM_HAS_FMEMOPEN)
-	SYSTEM_FMEMOPEN="no"
+	SYSTEM_FMEMOPEN=1
 	if test "${IS_MAC}" == "yes"; then
-		if [[ $(system_profiler SPSoftwareDataType | $(which grep) "System Version:" | sed -e "s/[[:space:]]*System Version: macOS //" | cut -d "." -f 2) -ge 13 ]]; then
-			SYSTEM_FMEMOPEN="yes"
-			AC_DEFINE([_SYSTEM_FMEMOPEN_], [1], [does system libc have fmemopen])
-		fi
-	fi
-	AM_CONDITIONAL([SYSTEM_HAS_FMEMOPEN], [test "${SYSTEM_FMEMOPEN}" == "yes"])
+		if [[ $(system_profiler SPSoftwareDataType | $(which grep) "System Version:" | sed -e "s/[[:space:]]*System Version: macOS //" | cut -d "." -f 2) -lt 13 ]]; then
+			SYSTEM_FMEMOPEN=0
+		fi
+	fi
+	AC_DEFINE(_SYSTEM_FMEMOPEN_, ${SYSTEM_FMEMOPEN}, [does system libc have fmemopen])
+	AM_CONDITIONAL([SYSTEM_HAS_FMEMOPEN], [test ${SYSTEM_FMEMOPEN} == 1])
 
 	IS_WINDOWS=no