diff --git a/Source/kwsys/SystemInformation.cxx b/Source/kwsys/SystemInformation.cxx
index 6c12355de7..f323efc4b0 100644
--- a/Source/kwsys/SystemInformation.cxx
+++ b/Source/kwsys/SystemInformation.cxx
@@ -4424,7 +4424,8 @@ bool SystemInformationImplementation::ParseSysCtl()
                       &count) == KERN_SUCCESS) {
     len = sizeof(value);
     err = sysctlbyname("hw.pagesize", &value, &len, KWSYS_NULLPTR, 0);
-    int64_t available_memory = vmstat.free_count * value;
+    int64_t available_memory =
+      (vmstat.free_count + vmstat.inactive_count) * value;
     this->AvailablePhysicalMemory =
       static_cast<size_t>(available_memory / 1048576);
   }