diff --git a/Signal/src/call/CallAudioService.swift b/Signal/src/call/CallAudioService.swift
index 9c1d05ee3..5d500c42f 100644
--- a/Signal/src/call/CallAudioService.swift
+++ b/Signal/src/call/CallAudioService.swift
@@ -55,6 +55,8 @@ import Foundation
     // MARK: - Service action handlers
 
     public func handleState(_ state: CallState) {
+        assert(Thread.isMainThread)
+
         Logger.verbose("\(TAG) in \(#function) new state: \(state)")
 
         switch state {