diff --git a/Evergreen/ProgressWindow/IndeterminateProgressWindowController.swift b/Evergreen/ProgressWindow/IndeterminateProgressWindowController.swift
index 644570852..b09b28894 100644
--- a/Evergreen/ProgressWindow/IndeterminateProgressWindowController.swift
+++ b/Evergreen/ProgressWindow/IndeterminateProgressWindowController.swift
@@ -8,7 +8,48 @@
 
 import Cocoa
 
-class IndeterminateProgressWindowController: NSWindowController {
+func runIndeterminateProgressWithMessage(_ message: String) {
+
+	IndeterminateProgressController.beginProgressWithMessage(message)
+}
+
+func stopIndeterminateProgress() {
+
+	IndeterminateProgressController.endProgress()
+}
+
+private final class IndeterminateProgressController {
+
+	static var windowController: IndeterminateProgressWindowController?
+	static var runningProgressWindow = false
+
+	static func beginProgressWithMessage(_ message: String) {
+
+		if runningProgressWindow {
+			assertionFailure("Expected !runningProgressWindow.")
+			endProgress()
+		}
+
+		runningProgressWindow = true
+		windowController = IndeterminateProgressWindowController(message: message)
+		NSApplication.shared.runModal(for: windowController!.window!)
+	}
+
+	static func endProgress() {
+
+		if !runningProgressWindow {
+			assertionFailure("Expected runningProgressWindow.")
+			return
+		}
+
+		runningProgressWindow = false
+		NSApplication.shared.stopModal()
+		windowController?.close()
+		windowController = nil
+	}
+}
+
+private final class IndeterminateProgressWindowController: NSWindowController {
 
 	@IBOutlet var messageLabel: NSTextField!
 	@IBOutlet var progressIndicator: NSProgressIndicator!
@@ -26,13 +67,5 @@ class IndeterminateProgressWindowController: NSWindowController {
 	}
 }
 
-func runIndeterminateProgressWithMessage(_ message: String) {
 
-	let windowController = IndeterminateProgressWindowController(message: message)
-	NSApplication.shared.runModal(for: windowController.window!)
-}
 
-func stopIndeterminateProgress() {
-
-	NSApplication.shared.stopModal()
-}