diff --git a/SignalServiceKit/src/Devices/OWSContactsOutputStream.m b/SignalServiceKit/src/Devices/OWSContactsOutputStream.m
index 9b6fb8f6f..e542c602e 100644
--- a/SignalServiceKit/src/Devices/OWSContactsOutputStream.m
+++ b/SignalServiceKit/src/Devices/OWSContactsOutputStream.m
@@ -61,6 +61,11 @@ NS_ASSUME_NONNULL_BEGIN
 
         if (disappearingMessagesConfiguration && disappearingMessagesConfiguration.isEnabled) {
             [contactBuilder setExpireTimer:disappearingMessagesConfiguration.durationSeconds];
+        } else {
+            // Rather than *not* set the field, we expicitly set it to 0 so desktop
+            // can easily distinguish between a modern client declaring "off" vs a
+            // legacy client "not specifying".
+            [contactBuilder setExpireTimer:0];
         }
     }
 
diff --git a/SignalServiceKit/src/Devices/OWSGroupsOutputStream.m b/SignalServiceKit/src/Devices/OWSGroupsOutputStream.m
index 0960bb163..8aa15079b 100644
--- a/SignalServiceKit/src/Devices/OWSGroupsOutputStream.m
+++ b/SignalServiceKit/src/Devices/OWSGroupsOutputStream.m
@@ -42,6 +42,11 @@ NS_ASSUME_NONNULL_BEGIN
 
         if (disappearingMessagesConfiguration && disappearingMessagesConfiguration.isEnabled) {
             [groupBuilder setExpireTimer:disappearingMessagesConfiguration.durationSeconds];
+        } else {
+            // Rather than *not* set the field, we expicitly set it to 0 so desktop
+            // can easily distinguish between a modern client declaring "off" vs a
+            // legacy client "not specifying".
+            [groupBuilder setExpireTimer:0];
         }
     }