diff --git a/Signal/src/AppDelegate.m b/Signal/src/AppDelegate.m
index 892f9c0fc..c82404617 100644
--- a/Signal/src/AppDelegate.m
+++ b/Signal/src/AppDelegate.m
@@ -1147,6 +1147,18 @@ static NSString *const kURLHostVerifyPrefix             = @"verify";
     [[OWSMessageReceiver sharedInstance] handleAnyUnprocessedEnvelopesAsync];
     [[OWSBatchMessageProcessor sharedInstance] handleAnyUnprocessedEnvelopesAsync];
 
+    if (!Environment.preferences.hasGeneratedThumbnails) {
+        [OWSPrimaryStorage.sharedManager.newDatabaseConnection
+            asyncReadWithBlock:^(YapDatabaseReadTransaction *_Nonnull transaction) {
+                [TSAttachmentStream enumerateCollectionObjectsUsingBlock:^(id _Nonnull obj, BOOL *_Nonnull stop){
+                    // no-op. It's sufficient to initWithCoder: each object.
+                }];
+            }
+            completionBlock:^{
+                [Environment.preferences setHasGeneratedThumbnails:YES];
+            }];
+    }
+
 #ifdef DEBUG
     // A bug in orphan cleanup could be disastrous so let's only
     // run it in DEBUG builds for a few releases.
diff --git a/SignalMessaging/utils/OWSPreferences.h b/SignalMessaging/utils/OWSPreferences.h
index a0c1884cb..a89fa53d1 100644
--- a/SignalMessaging/utils/OWSPreferences.h
+++ b/SignalMessaging/utils/OWSPreferences.h
@@ -61,6 +61,9 @@ extern NSString *const OWSPreferencesCallLoggingDidChangeNotification;
 - (void)setIOSUpgradeNagDate:(NSDate *)value;
 - (nullable NSDate *)iOSUpgradeNagDate;
 
+- (BOOL)hasGeneratedThumbnails;
+- (void)setHasGeneratedThumbnails:(BOOL)value;
+
 #pragma mark - Calling
 
 #pragma mark Callkit
diff --git a/SignalMessaging/utils/OWSPreferences.m b/SignalMessaging/utils/OWSPreferences.m
index 0ba08d806..dc11c5cf3 100644
--- a/SignalMessaging/utils/OWSPreferences.m
+++ b/SignalMessaging/utils/OWSPreferences.m
@@ -4,11 +4,11 @@
 
 #import "OWSPreferences.h"
 #import <SignalServiceKit/AppContext.h>
+#import <SignalServiceKit/NSNotificationCenter+OWS.h>
 #import <SignalServiceKit/NSUserDefaults+OWS.h>
 #import <SignalServiceKit/TSStorageHeaders.h>
 #import <SignalServiceKit/YapDatabaseConnection+OWS.h>
 #import <SignalServiceKit/YapDatabaseTransaction+OWS.h>
-#import <SignalServiceKit/NSNotificationCenter+OWS.h>
 
 NS_ASSUME_NONNULL_BEGIN
 
@@ -28,6 +28,7 @@ NSString *const OWSPreferencesKeyCallKitPrivacyEnabled = @"CallKitPrivacyEnabled
 NSString *const OWSPreferencesKeyCallsHideIPAddress = @"CallsHideIPAddress";
 NSString *const OWSPreferencesKeyRemoveMetadata = @"Remove Metadata Key";
 NSString *const OWSPreferencesKeyHasDeclinedNoContactsView = @"hasDeclinedNoContactsView";
+NSString *const OWSPreferencesKeyHasGeneratedThumbnails = @"OWSPreferencesKeyHasGeneratedThumbnails";
 NSString *const OWSPreferencesKeyIOSUpgradeNagDate = @"iOSUpgradeNagDate";
 NSString *const OWSPreferencesKey_IsReadyForAppExtensions = @"isReadyForAppExtensions_5";
 NSString *const OWSPreferencesKeySystemCallLogEnabled = @"OWSPreferencesKeySystemCallLogEnabled";
@@ -194,6 +195,18 @@ NSString *const OWSPreferencesKeySystemCallLogEnabled = @"OWSPreferencesKeySyste
     [self setValueForKey:OWSPreferencesKeyHasDeclinedNoContactsView toValue:@(value)];
 }
 
+- (BOOL)hasGeneratedThumbnails
+{
+    NSNumber *preference = [self tryGetValueForKey:OWSPreferencesKeyHasGeneratedThumbnails];
+    // Default to NO.
+    return preference ? [preference boolValue] : NO;
+}
+
+- (void)setHasGeneratedThumbnails:(BOOL)value
+{
+    [self setValueForKey:OWSPreferencesKeyHasGeneratedThumbnails toValue:@(value)];
+}
+
 - (void)setIOSUpgradeNagDate:(NSDate *)value
 {
     [self setValueForKey:OWSPreferencesKeyIOSUpgradeNagDate toValue:value];