diff --git a/src/SharpCompress/Compressors/PPMd/PpmdProperties.cs b/src/SharpCompress/Compressors/PPMd/PpmdProperties.cs
index e4d52c17..708bdd36 100644
--- a/src/SharpCompress/Compressors/PPMd/PpmdProperties.cs
+++ b/src/SharpCompress/Compressors/PPMd/PpmdProperties.cs
@@ -55,13 +55,14 @@ public class PpmdProperties
         get => _allocatorSize;
         set
         {
-            _allocatorSize = value;
             if (Version == PpmdVersion.I1)
             {
                 _allocator ??= new Allocator();
 
-                _allocator.Start(_allocatorSize);
+                _allocator.Start(value);
             }
+            // Keep the serialized properties in sync with the allocator if Start rejects the size.
+            _allocatorSize = value;
         }
     }
 
diff --git a/tests/SharpCompress.Test/Streams/DictionarySizeLimitTests.cs b/tests/SharpCompress.Test/Streams/DictionarySizeLimitTests.cs
index 6b5e853e..2619761b 100644
--- a/tests/SharpCompress.Test/Streams/DictionarySizeLimitTests.cs
+++ b/tests/SharpCompress.Test/Streams/DictionarySizeLimitTests.cs
@@ -154,6 +154,23 @@ public class DictionarySizeLimitTests : TestBase
         Assert.Throws<InvalidFormatException>(() => new PpmdProperties(256 << 20, 6));
     }
 
+    [Fact]
+    public void Ppmd_Properties_Preserve_Size_After_Rejected_Change()
+    {
+        using var limits = new DictionarySizeLimitScope();
+        DictionarySizeLimits.Ppmd = 2 << 20;
+        var properties = new PpmdProperties(1 << 20, 6);
+        var originalHeader = properties.Properties;
+
+        Assert.Throws<InvalidFormatException>(() => properties.AllocatorSize = 3 << 20);
+        Assert.Equal(1 << 20, properties.AllocatorSize);
+        Assert.Equal(originalHeader, properties.Properties);
+
+        properties.AllocatorSize = 2 << 20;
+        Assert.Equal(2 << 20, properties.AllocatorSize);
+        Assert.Equal(2 << 20, new PpmdProperties(properties.Properties).AllocatorSize);
+    }
+
     [Theory]
     [InlineData(false)]
     [InlineData(true)]