diff --git a/src/ZString.Unity/Assets/Scripts/ZString/Utf16ValueStringBuilder.cs b/src/ZString.Unity/Assets/Scripts/ZString/Utf16ValueStringBuilder.cs
index df6ec3b..b1855b4 100644
--- a/src/ZString.Unity/Assets/Scripts/ZString/Utf16ValueStringBuilder.cs
+++ b/src/ZString.Unity/Assets/Scripts/ZString/Utf16ValueStringBuilder.cs
@@ -465,23 +465,25 @@ public void Replace(ReadOnlySpan<char> oldValue, ReadOnlySpan<char> newValue, in
             buffer.AsSpan(0, startIndex).CopyTo(newBuffer);
             int newBufferIndex = startIndex;
 
-            for (int i = startIndex; i < endIndex; i += oldValue.Length)
+            int readIndex = startIndex;
+            for (; readIndex < endIndex; readIndex += oldValue.Length)
             {
-                var span = readOnlySpan.Slice(i, endIndex - i);
+                var span = readOnlySpan.Slice(readIndex, endIndex - readIndex);
                 var pos = span.IndexOf(oldValue, StringComparison.Ordinal);
                 if (pos == -1)
                 {
-                    var remain = readOnlySpan.Slice(i);
-                    remain.CopyTo(newBuffer.AsSpan(newBufferIndex));
-                    newBufferIndex += remain.Length;
                     break;
                 }
-                readOnlySpan.Slice(i, pos).CopyTo(newBuffer.AsSpan(newBufferIndex));
+                readOnlySpan.Slice(readIndex, pos).CopyTo(newBuffer.AsSpan(newBufferIndex));
                 newValue.CopyTo(newBuffer.AsSpan(newBufferIndex + pos));
                 newBufferIndex += pos + newValue.Length;
-                i += pos;
+                readIndex += pos;
             }
 
+            var remain = readOnlySpan.Slice(readIndex);
+            remain.CopyTo(newBuffer.AsSpan(newBufferIndex));
+            newBufferIndex += remain.Length;
+
             if (buffer!.Length != ThreadStaticBufferSize)
             {
                 ArrayPool<char>.Shared.Return(buffer);
diff --git a/src/ZString/Utf16ValueStringBuilder.cs b/src/ZString/Utf16ValueStringBuilder.cs
index df6ec3b..b1855b4 100644
--- a/src/ZString/Utf16ValueStringBuilder.cs
+++ b/src/ZString/Utf16ValueStringBuilder.cs
@@ -465,23 +465,25 @@ public void Replace(ReadOnlySpan<char> oldValue, ReadOnlySpan<char> newValue, in
             buffer.AsSpan(0, startIndex).CopyTo(newBuffer);
             int newBufferIndex = startIndex;
 
-            for (int i = startIndex; i < endIndex; i += oldValue.Length)
+            int readIndex = startIndex;
+            for (; readIndex < endIndex; readIndex += oldValue.Length)
             {
-                var span = readOnlySpan.Slice(i, endIndex - i);
+                var span = readOnlySpan.Slice(readIndex, endIndex - readIndex);
                 var pos = span.IndexOf(oldValue, StringComparison.Ordinal);
                 if (pos == -1)
                 {
-                    var remain = readOnlySpan.Slice(i);
-                    remain.CopyTo(newBuffer.AsSpan(newBufferIndex));
-                    newBufferIndex += remain.Length;
                     break;
                 }
-                readOnlySpan.Slice(i, pos).CopyTo(newBuffer.AsSpan(newBufferIndex));
+                readOnlySpan.Slice(readIndex, pos).CopyTo(newBuffer.AsSpan(newBufferIndex));
                 newValue.CopyTo(newBuffer.AsSpan(newBufferIndex + pos));
                 newBufferIndex += pos + newValue.Length;
-                i += pos;
+                readIndex += pos;
             }
 
+            var remain = readOnlySpan.Slice(readIndex);
+            remain.CopyTo(newBuffer.AsSpan(newBufferIndex));
+            newBufferIndex += remain.Length;
+
             if (buffer!.Length != ThreadStaticBufferSize)
             {
                 ArrayPool<char>.Shared.Return(buffer);
diff --git a/tests/ZString.Tests/ReplaceTest.cs b/tests/ZString.Tests/ReplaceTest.cs
index 8b25eb1..70bc269 100644
--- a/tests/ZString.Tests/ReplaceTest.cs
+++ b/tests/ZString.Tests/ReplaceTest.cs
@@ -87,6 +87,23 @@ public void ReplaceStringTest()
             }
         }
         
+        [Theory]
+        [InlineData("abcTAIL", "bc", "X", 1, 2)]
+        [InlineData("abcTAIL", "bc", "", 1, 2)]
+        [InlineData("abcTAIL", "bc", "longer", 1, 2)]
+        [InlineData("abcbcTAIL", "bc", "X", 1, 4)]
+        [InlineData("abczTAIL", "bc", "X", 1, 3)]
+        [InlineData("abc", "bc", "X", 1, 2)]
+        public void ReplacePreservesSuffix(string text, string oldValue, string newValue, int startIndex, int count)
+        {
+            using (var zsb = ZString.CreateStringBuilder())
+            {
+                zsb.Append(text);
+                zsb.Replace(oldValue, newValue, startIndex, count);
+                zsb.ToString().Should().Be(new StringBuilder(text).Replace(oldValue, newValue, startIndex, count).ToString());
+            }
+        }
+
         [Fact]
         public void NotMatchTest()
         {