diff --git a/aider/coders/editblock_coder.py b/aider/coders/editblock_coder.py
index f05a60c4d..6e94f1c3b 100644
--- a/aider/coders/editblock_coder.py
+++ b/aider/coders/editblock_coder.py
@@ -404,94 +404,69 @@ def strip_filename(filename, fence):
 
 
 def find_original_update_blocks(content, fence=DEFAULT_FENCE):
-    # make sure we end with a newline, otherwise the regex will miss <<UPD on the last line
-    if not content.endswith("\n"):
-        content = content + "\n"
-
-    pieces = re.split(split_re, content)
-
-    pieces.reverse()
-    processed = []
-
-    # Keep using the same filename in cases where GPT produces an edit block
-    # without a filename.
+    lines = content.splitlines(keepends=True)
+    i = 0
     current_filename = None
-    try:
-        while pieces:
-            cur = pieces.pop()
-            dump(repr(cur))
 
-            # Check for various shell code blocks
-            shell_starts = [
-                "```bash",
-                "```sh",
-                "```shell",  # Unix-like shells
-                "```cmd",
-                "```batch",  # Windows Command Prompt
-                "```powershell",
-                "```ps1",  # Windows PowerShell
-                "```zsh",  # Z shell
-                "```fish",  # Friendly Interactive Shell
-                "```ksh",  # Korn Shell
-                "```csh",
-                "```tcsh",  # C Shell and TENEX C Shell
-            ]
-            if any(cur.strip().startswith(start) for start in shell_starts):
-                shell_content = []
-                while pieces and not pieces[-1].strip().startswith("```"):
-                    shell_content.append(pieces.pop())
-                if pieces and pieces[-1].strip().startswith("```"):
-                    pieces.pop()  # Remove the closing ```
-                shell_type = cur.strip().split("```")[1]
-                yield f"{shell_type}_command", "".join(shell_content)
-                continue
+    while i < len(lines):
+        line = lines[i]
 
-            if cur in (DIVIDER, UPDATED):
-                processed.append(cur)
-                raise ValueError(f"Unexpected {cur}")
+        # Check for shell code blocks
+        shell_starts = [
+            "```bash", "```sh", "```shell", "```cmd", "```batch",
+            "```powershell", "```ps1", "```zsh", "```fish", "```ksh",
+            "```csh", "```tcsh"
+        ]
+        if any(line.strip().startswith(start) for start in shell_starts):
+            shell_type = line.strip().split("```")[1]
+            shell_content = []
+            i += 1
+            while i < len(lines) and not lines[i].strip().startswith("```"):
+                shell_content.append(lines[i])
+                i += 1
+            if i < len(lines) and lines[i].strip().startswith("```"):
+                i += 1  # Skip the closing ```
+            yield f"{shell_type}_command", "".join(shell_content)
+            continue
 
-            if cur.strip() != HEAD:
-                processed.append(cur)
-                continue
+        # Check for SEARCH/REPLACE blocks
+        if line.strip() == HEAD:
+            try:
+                filename = find_filename(lines[max(0, i-3):i], fence)
+                if not filename:
+                    if current_filename:
+                        filename = current_filename
+                    else:
+                        raise ValueError(missing_filename_err.format(fence=fence))
 
-            processed.append(cur)  # original_marker
+                current_filename = filename
 
-            filename = find_filename(processed[-2].splitlines(), fence)
-            if not filename:
-                if current_filename:
-                    filename = current_filename
-                else:
-                    raise ValueError(missing_filename_err.format(fence=fence))
+                original_text = []
+                i += 1
+                while i < len(lines) and not lines[i].strip() == DIVIDER:
+                    original_text.append(lines[i])
+                    i += 1
 
-            current_filename = filename
+                if i >= len(lines) or lines[i].strip() != DIVIDER:
+                    raise ValueError(f"Expected `{DIVIDER}`")
 
-            original_text = pieces.pop()
-            processed.append(original_text)
+                updated_text = []
+                i += 1
+                while i < len(lines) and not lines[i].strip() == UPDATED:
+                    updated_text.append(lines[i])
+                    i += 1
 
-            divider_marker = pieces.pop()
-            processed.append(divider_marker)
-            if divider_marker.strip() != DIVIDER:
-                raise ValueError(f"Expected `{DIVIDER}` not {divider_marker.strip()}")
+                if i >= len(lines) or lines[i].strip() != UPDATED:
+                    raise ValueError(f"Expected `{UPDATED}`")
 
-            updated_text = pieces.pop()
-            processed.append(updated_text)
+                yield filename, "".join(original_text), "".join(updated_text)
 
-            updated_marker = pieces.pop()
-            processed.append(updated_marker)
-            if updated_marker.strip() != UPDATED:
-                raise ValueError(f"Expected `{UPDATED}` not `{updated_marker.strip()}")
+            except ValueError as e:
+                processed = "".join(lines[:i+1])
+                err = e.args[0]
+                raise ValueError(f"{processed}\n^^^ {err}")
 
-            yield filename, original_text, updated_text
-    except ValueError as e:
-        processed = "".join(processed)
-        err = e.args[0]
-        raise ValueError(f"{processed}\n^^^ {err}")
-    except IndexError:
-        processed = "".join(processed)
-        raise ValueError(f"{processed}\n^^^ Incomplete SEARCH/REPLACE block.")
-    except Exception:
-        processed = "".join(processed)
-        raise ValueError(f"{processed}\n^^^ Error parsing SEARCH/REPLACE block.")
+        i += 1
 
 
 def find_filename(lines, fence):