diff --git a/src/FilterLists.Services/SnapshotService/RawRuleLinterExtensions.cs b/src/FilterLists.Services/SnapshotService/RawRuleLinterExtensions.cs
index f2b857cd3..1d4f66932 100644
--- a/src/FilterLists.Services/SnapshotService/RawRuleLinterExtensions.cs
+++ b/src/FilterLists.Services/SnapshotService/RawRuleLinterExtensions.cs
@@ -2,7 +2,7 @@
 {
     public static class RawRuleLinterExtensions
     {
-        public static string LintStringForMySql(this string rule)
+        public static string LintRawRule(this string rule)
         {
             rule = rule?.TrimLeadingAndTrailingWhitespace();
             rule = rule?.DropIfEmpty();
diff --git a/src/FilterLists.Services/SnapshotService/SnapshotBatchDe.cs b/src/FilterLists.Services/SnapshotService/SnapshotBatchDe.cs
index 80cb4dcbb..09d0e956f 100644
--- a/src/FilterLists.Services/SnapshotService/SnapshotBatchDe.cs
+++ b/src/FilterLists.Services/SnapshotService/SnapshotBatchDe.cs
@@ -13,8 +13,7 @@ public class SnapshotBatchDe
         private readonly FilterListsDbContext dbContext;
         private readonly IEnumerable<string> rawRules;
         private readonly Snapshot snapshot;
-        private IEnumerable<Rule> newSnapshotRules;
-        private IEnumerable<Rule> preExistingSnapshotRules;
+        private IQueryable<Rule> rules;
 
         public SnapshotBatchDe(FilterListsDbContext dbContext, Snapshot snapshot, IEnumerable<string> rawRules)
         {
@@ -23,31 +22,26 @@ public SnapshotBatchDe(FilterListsDbContext dbContext, Snapshot snapshot, IEnume
             this.rawRules = rawRules;
         }
 
-        //TODO: support de-duplicated SnapshotRule
         public async Task SaveSnapshotBatchAsync()
         {
-            AddNewRules();
+            AddRules();
             AddSnapshotRules();
             await dbContext.SaveChangesAsync();
         }
 
-        private void AddNewRules()
+        private void AddRules()
         {
-            preExistingSnapshotRules = dbContext.Rules.Where(rule => rawRules.Contains(rule.Raw));
-            var newSnapshotRawRules = rawRules.Except(preExistingSnapshotRules.Select(x => x.Raw));
-            newSnapshotRules = newSnapshotRawRules.Select(newSnapshotRawRule => new Rule {Raw = newSnapshotRawRule})
-                                                  .ToList();
-            dbContext.Rules.AddRange(newSnapshotRules);
+            var existingRules = dbContext.Rules.Where(rule => rawRules.Contains(rule.Raw));
+            var newRawRules = rawRules.Except(existingRules.Select(x => x.Raw));
+            var newRules = newRawRules.Select(newRawRule => new Rule {Raw = newRawRule}).ToList();
+            dbContext.Rules.AddRange(newRules);
+            rules = existingRules.Concat(newRules);
         }
 
         private void AddSnapshotRules()
         {
-            if (snapshot.AddedSnapshotRules == null)
-                snapshot.AddedSnapshotRules = new List<SnapshotRule>();
-            snapshot.AddedSnapshotRules.AddRange(preExistingSnapshotRules
-                                            .Concat(newSnapshotRules)
-                                            .Select(rule => new SnapshotRule {Rule = rule, AddedBySnapshot = snapshot})
-                                            .ToList());
+            var snapshotRules = rules.Select(rule => new SnapshotRule {Rule = rule, AddedBySnapshot = snapshot});
+            snapshot.AddedSnapshotRules.AddRange(snapshotRules);
         }
     }
 }
\ No newline at end of file
diff --git a/src/FilterLists.Services/SnapshotService/SnapshotDe.cs b/src/FilterLists.Services/SnapshotService/SnapshotDe.cs
index 07906e849..a9a445fe0 100644
--- a/src/FilterLists.Services/SnapshotService/SnapshotDe.cs
+++ b/src/FilterLists.Services/SnapshotService/SnapshotDe.cs
@@ -24,12 +24,21 @@ public SnapshotDe(FilterListsDbContext dbContext, FilterListViewUrlDto list)
         }
 
         public async Task SaveSnapshotAsync()
+        {
+            var content = await CaptureSnapshot();
+            if (content != null)
+            {
+                await SaveSnapshotInBatches(content);
+                await DedupSnapshotRules();
+            }
+        }
+
+        private async Task<string> CaptureSnapshot()
         {
             await AddSnapshot();
             var content = await TryGetContent();
             await dbContext.SaveChangesAsync();
-            if (content != null)
-                await SaveSnapshotInBatches(content);
+            return content;
         }
 
         private async Task AddSnapshot()
@@ -80,7 +89,7 @@ private static IEnumerable<string> GetRawRules(string content)
         {
             var rawRules = content.Split(new[] {"\r\n", "\r", "\n"}, StringSplitOptions.RemoveEmptyEntries);
             for (var i = 0; i < rawRules.Length; i++)
-                rawRules[i] = rawRules[i].LintStringForMySql();
+                rawRules[i] = rawRules[i].LintRawRule();
             return new HashSet<string>(rawRules.Where(x => x != null));
         }
 
@@ -95,5 +104,25 @@ private static async Task SaveSnapshotBatches(IEnumerable<SnapshotBatchDe> snaps
             foreach (var snapshotBatch in snapshotBatches)
                 await snapshotBatch.SaveSnapshotBatchAsync();
         }
+
+        //TODO: test
+        private async Task DedupSnapshotRules()
+        {
+            var currentSnapshotRules =
+                dbContext.SnapshotRules.Where(x => x.AddedBySnapshot == snapshot).Select(x => x.Rule);
+
+            var existingSnapshotRules = dbContext.SnapshotRules.Where(x =>
+                x.AddedBySnapshot.FilterListId == list.Id &&
+                x.AddedBySnapshot != snapshot &&
+                x.RemovedBySnapshot == null);
+
+            var removedSnapshotRules = existingSnapshotRules.Where(x => !currentSnapshotRules.Contains(x.Rule));
+
+            removedSnapshotRules.ToList().ForEach(x => x.RemovedBySnapshot = snapshot);
+
+            //TODO: delete any added SnapshotRules that were already in a previous snapshot and were not marked as removed
+
+            await dbContext.SaveChangesAsync();
+        }
     }
 }
\ No newline at end of file
diff --git a/src/FilterLists.Services/SnapshotService/SnapshotService.cs b/src/FilterLists.Services/SnapshotService/SnapshotService.cs
index cb330b538..768031648 100644
--- a/src/FilterLists.Services/SnapshotService/SnapshotService.cs
+++ b/src/FilterLists.Services/SnapshotService/SnapshotService.cs
@@ -18,6 +18,7 @@ public SnapshotService(FilterListsDbContext dbContext)
 
         public async Task CaptureSnapshotsAsync(int batchSize)
         {
+            //TODO: rollback changes from recent snapshots if they were interrupted
             var lists = await GetLeastRecentlyCapturedLists(batchSize);
             var snapshots = GetSnapshots(lists);
             await SaveSnapshots(snapshots);