diff --git a/src/anthropic/lib/tools/_beta_builtin_memory_tool.py b/src/anthropic/lib/tools/_beta_builtin_memory_tool.py
index b995fbb3d..5242469fc 100644
--- a/src/anthropic/lib/tools/_beta_builtin_memory_tool.py
+++ b/src/anthropic/lib/tools/_beta_builtin_memory_tool.py
@@ -547,7 +547,7 @@ def insert(self, command: BetaMemoryTool20250818InsertCommand) -> str:
             raise ToolError(f"The path {command.path} is not a file.")
 
         content = _read_file_content(full_path, command.path)
-        lines = content.splitlines()
+        lines = content.split("\n")
 
         if command.insert_line < 0 or command.insert_line > len(lines):
             raise ToolError(
@@ -848,7 +848,7 @@ async def insert(self, command: BetaMemoryTool20250818InsertCommand) -> str:
             raise ToolError(f"The path {command.path} is not a file.")
 
         content = await _async_read_file_content(full_path, command.path)
-        lines = content.splitlines()
+        lines = content.split("\n")
 
         if command.insert_line < 0 or command.insert_line > len(lines):
             raise ToolError(
diff --git a/tests/lib/tools/memory_tools/test_filesystem.py b/tests/lib/tools/memory_tools/test_filesystem.py
index 0ab3c8fa9..1f0fb083c 100644
--- a/tests/lib/tools/memory_tools/test_filesystem.py
+++ b/tests/lib/tools/memory_tools/test_filesystem.py
@@ -372,6 +372,32 @@ def test_insert_error_for_invalid_insert_line(
                 )
             )
 
+    def test_insert_preserves_non_newline_line_boundaries(
+        self, sync_local_filesystem_tool: BetaLocalFilesystemMemoryTool
+    ) -> None:
+        # U+2028 and form-feed are line boundaries for str.splitlines() but not for "\n".
+        # view()/str_replace() split on "\n", so insert() must too, otherwise these
+        # characters are silently rewritten to "\n" and the text lands at the wrong line.
+        sync_local_filesystem_tool.create(
+            BetaMemoryTool20250818CreateCommand(
+                command="create", file_text="alpha\u2028beta\x0cgamma", path="/memories/insert_unicode_test.txt"
+            )
+        )
+
+        view_result = sync_local_filesystem_tool.view(
+            BetaMemoryTool20250818ViewCommand(command="view", path="/memories/insert_unicode_test.txt")
+        )
+        assert len(view_result.split(":\n", 1)[1].split("\n")) == 1
+
+        sync_local_filesystem_tool.insert(
+            BetaMemoryTool20250818InsertCommand(
+                command="insert", path="/memories/insert_unicode_test.txt", insert_line=1, insert_text="INSERTED"
+            )
+        )
+
+        dir_snapshot = get_directory_snapshot(str(sync_local_filesystem_tool.base_path))
+        assert dir_snapshot == {"memories/insert_unicode_test.txt": "alpha\u2028beta\x0cgamma\nINSERTED\n"}
+
     def test_delete(self, sync_local_filesystem_tool: BetaLocalFilesystemMemoryTool) -> None:
         sync_local_filesystem_tool.create(
             BetaMemoryTool20250818CreateCommand(
@@ -862,6 +888,32 @@ async def test_insert_error_for_invalid_insert_line(
                 )
             )
 
+    async def test_insert_preserves_non_newline_line_boundaries(
+        self, async_local_filesystem_tool: BetaAsyncLocalFilesystemMemoryTool
+    ) -> None:
+        # U+2028 and form-feed are line boundaries for str.splitlines() but not for "\n".
+        # view()/str_replace() split on "\n", so insert() must too, otherwise these
+        # characters are silently rewritten to "\n" and the text lands at the wrong line.
+        await async_local_filesystem_tool.create(
+            BetaMemoryTool20250818CreateCommand(
+                command="create", file_text="alpha\u2028beta\x0cgamma", path="/memories/insert_unicode_test.txt"
+            )
+        )
+
+        view_result = await async_local_filesystem_tool.view(
+            BetaMemoryTool20250818ViewCommand(command="view", path="/memories/insert_unicode_test.txt")
+        )
+        assert len(view_result.split(":\n", 1)[1].split("\n")) == 1
+
+        await async_local_filesystem_tool.insert(
+            BetaMemoryTool20250818InsertCommand(
+                command="insert", path="/memories/insert_unicode_test.txt", insert_line=1, insert_text="INSERTED"
+            )
+        )
+
+        dir_snapshot = get_directory_snapshot(str(async_local_filesystem_tool.base_path))
+        assert dir_snapshot == {"memories/insert_unicode_test.txt": "alpha\u2028beta\x0cgamma\nINSERTED\n"}
+
     async def test_delete(self, async_local_filesystem_tool: BetaAsyncLocalFilesystemMemoryTool) -> None:
         await async_local_filesystem_tool.create(
             BetaMemoryTool20250818CreateCommand(