diff --git a/server/disk_avail.go b/server/disk_avail.go
new file mode 100644
index 00000000..90157fe7
--- /dev/null
+++ b/server/disk_avail.go
@@ -0,0 +1,37 @@
+// Copyright 2020 The NATS Authors
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+// http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+// +build !windows
+
+package server
+
+import (
+	"os"
+	"syscall"
+)
+
+func diskAvailable(storeDir string) int64 {
+	var ba int64
+	if _, err := os.Stat(storeDir); os.IsNotExist(err) {
+		os.MkdirAll(storeDir, 0755)
+	}
+	var fs syscall.Statfs_t
+	if err := syscall.Statfs(storeDir, &fs); err == nil {
+		// Estimate 75% of available storage.
+		ba = int64(fs.Bavail * uint64(fs.Bsize) / 4 * 3)
+	} else {
+		// Used 1TB default as a guess if all else fails.
+		ba = JetStreamMaxStoreDefault
+	}
+	return ba
+}
diff --git a/server/disk_avail_windows.go b/server/disk_avail_windows.go
new file mode 100644
index 00000000..0e057087
--- /dev/null
+++ b/server/disk_avail_windows.go
@@ -0,0 +1,21 @@
+// Copyright 2020 The NATS Authors
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+// http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+// +build windows
+
+package server
+
+// TODO(dlc) - See if there is a version of this for windows.
+func diskAvailable(storeDir string) int64 {
+	return JetStreamMaxStoreDefault
+}
diff --git a/server/jetstream.go b/server/jetstream.go
index bc0eb12c..10b5dfd7 100644
--- a/server/jetstream.go
+++ b/server/jetstream.go
@@ -26,7 +26,6 @@ import (
 	"strconv"
 	"strings"
 	"sync"
-	"syscall"
 
 	"github.com/minio/highwayhash"
 	"github.com/nats-io/nats-server/v2/server/sysmem"
@@ -944,17 +943,7 @@ func (s *Server) dynJetStreamConfig(storeDir string, maxStore int64) *JetStreamC
 	if maxStore > 0 {
 		jsc.MaxStore = maxStore
 	} else {
-		if _, err := os.Stat(jsc.StoreDir); os.IsNotExist(err) {
-			os.MkdirAll(jsc.StoreDir, 0755)
-		}
-		var fs syscall.Statfs_t
-		if err := syscall.Statfs(jsc.StoreDir, &fs); err == nil {
-			// Estimate 75% of available storage.
-			jsc.MaxStore = int64(fs.Bavail * uint64(fs.Bsize) / 4 * 3)
-		} else {
-			// Used 1TB default as a guess if all else fails.
-			jsc.MaxStore = JetStreamMaxStoreDefault
-		}
+		jsc.MaxStore = diskAvailable(jsc.StoreDir)
 	}
 	// Estimate to 75% of total memory if we can determine system memory.
 	if sysMem := sysmem.Memory(); sysMem > 0 {