diff --git a/SignalServiceKit/src/Contacts/OWSContactDiscoveryOperation.swift b/SignalServiceKit/src/Contacts/OWSContactDiscoveryOperation.swift
index d630980f8..018054f7c 100644
--- a/SignalServiceKit/src/Contacts/OWSContactDiscoveryOperation.swift
+++ b/SignalServiceKit/src/Contacts/OWSContactDiscoveryOperation.swift
@@ -5,7 +5,7 @@
 import Foundation
 
 @objc(OWSContactDiscoveryOperation)
-class ContactDiscoveryOperation: OWSOperation {
+class ContactDiscoveryOperation: OWSOperation, LegacyContactDiscoveryBatchOperationDelegate {
 
     let batchSize = 2048
     let recipientIdsToLookup: [String]
@@ -23,6 +23,7 @@ class ContactDiscoveryOperation: OWSOperation {
         Logger.debug("\(logTag) in \(#function) with recipientIdsToLookup: \(recipientIdsToLookup.count)")
         for batchIds in recipientIdsToLookup.chunked(by: batchSize) {
             let batchOperation = LegacyContactDiscoveryBatchOperation(recipientIdsToLookup: batchIds)
+            batchOperation.delegate = self
             self.addDependency(batchOperation)
         }
     }
@@ -44,11 +45,24 @@ class ContactDiscoveryOperation: OWSOperation {
 
         self.reportSuccess()
     }
+
+    // MARK: LegacyContactDiscoveryBatchOperationDelegate
+    func contactDiscoverBatchOperation(_ contactDiscoverBatchOperation: LegacyContactDiscoveryBatchOperation, didFailWithError error: Error) {
+        Logger.debug("\(logTag) in \(#function) canceling self and all dependencies.")
+
+        self.dependencies.forEach { $0.cancel() }
+        self.cancel()
+    }
+}
+
+protocol LegacyContactDiscoveryBatchOperationDelegate: class {
+    func contactDiscoverBatchOperation(_ contactDiscoverBatchOperation: LegacyContactDiscoveryBatchOperation, didFailWithError error: Error)
 }
 
 class LegacyContactDiscoveryBatchOperation: OWSOperation {
 
     var registeredRecipientIds: Set<String>
+    weak var delegate: LegacyContactDiscoveryBatchOperationDelegate?
 
     private let recipientIdsToLookup: [String]
     private var networkManager: TSNetworkManager {
@@ -72,10 +86,17 @@ class LegacyContactDiscoveryBatchOperation: OWSOperation {
     override func run() {
         Logger.debug("\(logTag) in \(#function)")
 
+        guard !isCancelled else {
+            Logger.info("\(logTag) in \(#function) no work to do, since we were canceled")
+            self.reportCancelled()
+            return
+        }
+
         var phoneNumbersByHashes: [String: String] = [:]
 
         for recipientId in recipientIdsToLookup {
             let hash = Cryptography.truncatedSHA1Base64EncodedWithoutPadding(recipientId)
+            assert(phoneNumbersByHashes[hash] == nil)
             phoneNumbersByHashes[hash] = recipientId
         }
 
@@ -121,6 +142,11 @@ class LegacyContactDiscoveryBatchOperation: OWSOperation {
         CDSFeedbackOperation.operationQueue.addOperations([newCDSBatchOperation, cdsFeedbackOperation], waitUntilFinished: false)
     }
 
+    // Called at most one time.
+    override func didFail(error: Error) {
+        self.delegate?.contactDiscoverBatchOperation(self, didFailWithError: error)
+    }
+
     // MARK: Private Helpers
 
     private func parse(response: Any?, phoneNumbersByHashes: [String: String]) throws -> Set<String> {
diff --git a/SignalServiceKit/src/Util/OWSOperation.h b/SignalServiceKit/src/Util/OWSOperation.h
index c86c90394..55e30bed0 100644
--- a/SignalServiceKit/src/Util/OWSOperation.h
+++ b/SignalServiceKit/src/Util/OWSOperation.h
@@ -42,17 +42,27 @@ typedef NS_ENUM(NSInteger, OWSOperationState) {
 // Called at most one time.
 - (void)didSucceed;
 
+// Called at most one time.
+- (void)didCancel;
+
 // Called at most one time, once retry is no longer possible.
 - (void)didFailWithError:(NSError *)error NS_SWIFT_NAME(didFail(error:));
 
 #pragma mark - Success/Error - Do Not Override
 
-// Complete the operation successfully.
-// Should be called at most once per operation instance.
-// You must ensure that `run` cannot fail after calling `reportSuccess`.
+// Report that the operation completed successfully.
+//
+// Each invocation of `run` must make exactly one call to one of: `reportSuccess`, `reportCancelled`, or `reportError:`
 - (void)reportSuccess;
 
-// Should be called at most once per `run`.
+// Call this when you abort before completion due to being cancelled.
+//
+// Each invocation of `run` must make exactly one call to one of: `reportSuccess`, `reportCancelled`, or `reportError:`
+- (void)reportCancelled;
+
+// Report that the operation failed to complete due to an error.
+//
+// Each invocation of `run` must make exactly one call to one of: `reportSuccess`, `reportCancelled`, or `reportError:`
 // You must ensure that `run` cannot succeed after calling `reportError`, e.g. generally you'll write something like
 // this:
 //
diff --git a/SignalServiceKit/src/Util/OWSOperation.m b/SignalServiceKit/src/Util/OWSOperation.m
index d70cbb4c6..da9fa32e8 100644
--- a/SignalServiceKit/src/Util/OWSOperation.m
+++ b/SignalServiceKit/src/Util/OWSOperation.m
@@ -81,6 +81,13 @@ NSString *const OWSOperationKeyIsFinished = @"isFinished";
     // Override in subclass if necessary
 }
 
+// Called at most one time.
+- (void)didCancel
+{
+    // no-op
+    // Override in subclass if necessary
+}
+
 // Called at most one time, once retry is no longer possible.
 - (void)didFailWithError:(NSError *)error
 {
@@ -113,6 +120,14 @@ NSString *const OWSOperationKeyIsFinished = @"isFinished";
     [self markAsComplete];
 }
 
+// These methods are not intended to be subclassed
+- (void)reportCancelled
+{
+    DDLogDebug(@"%@ cancelled.", self.logTag);
+    [self didCancel];
+    [self markAsComplete];
+}
+
 - (void)reportError:(NSError *)error
 {
     DDLogDebug(@"%@ reportError: %@, fatal?: %d, retryable?: %d, remainingRetries: %lu",