diff --git a/data_prep/introspector.py b/data_prep/introspector.py
index 123154ac2b..bcbd859100 100755
--- a/data_prep/introspector.py
+++ b/data_prep/introspector.py
@@ -228,6 +228,15 @@ def query_introspector_cfg(project: str) -> dict:
   return _get_data(resp, 'project', {})
 
 
+def query_introspector_source_file_path(project: str, func_sig: str) -> str:
+  """Queries FuzzIntrospector API for file path of |func_sig|."""
+  resp = _query_introspector(INTROSPECTOR_FUNCTION_SOURCE, {
+      'project': project,
+      'function_signature': func_sig
+  })
+  return _get_data(resp, 'filepath', '')
+
+
 def query_introspector_function_source(project: str, func_sig: str) -> str:
   """Queries FuzzIntrospector API for source code of |func_sig|."""
   resp = _query_introspector(INTROSPECTOR_FUNCTION_SOURCE, {
diff --git a/data_prep/project_context/context_introspector.py b/data_prep/project_context/context_introspector.py
index 0e094910ed..ccecdc630c 100644
--- a/data_prep/project_context/context_introspector.py
+++ b/data_prep/project_context/context_introspector.py
@@ -3,6 +3,7 @@
 
 import logging
 import os
+from difflib import SequenceMatcher
 from typing import Any
 
 from data_prep import introspector
@@ -217,3 +218,37 @@ def get_type_def(self, type_name: str) -> str:
           type_names.append(new_type_name)
 
     return type_def
+
+  def get_similar_header_file_paths(self, wrong_file: str) -> list[str]:
+    """Retrieves and finds 5 header file names closest to |wrong_name|."""
+    header_list = introspector.query_introspector_header_files(
+        self._benchmark.project)
+    candidate_header_scores = {
+        header:
+            SequenceMatcher(lambda x: x in ['_', '/', '-', '.'], wrong_file,
+                            header).ratio() for header in header_list
+    }
+    candidate_headers = sorted(candidate_header_scores,
+                               key=lambda x: candidate_header_scores[x],
+                               reverse=True)
+    return candidate_headers[:5]
+
+  def get_target_function_file_path(self) -> str:
+    """Retrieves the header/source file of the function under test."""
+    # Step 1: Find a header file that shares the same name as the source file.
+    # TODO: Make this more robust, e.g., when header file and base file do not
+    # share the same basename.
+    source_file = introspector.query_introspector_source_file_path(
+        self._benchmark.project, self._benchmark.function_signature)
+    source_file_base, _ = os.path.splitext(os.path.basename(source_file))
+    header_list = introspector.query_introspector_header_files(
+        self._benchmark.project)
+    candidate_headers = [
+        header for header in header_list
+        if os.path.basename(header).startswith(source_file_base)
+    ]
+    if candidate_headers:
+      return candidate_headers[0]
+
+    # Step 2: Use the source file If it does not have a same-name-header.
+    return source_file
diff --git a/llm_toolkit/code_fixer.py b/llm_toolkit/code_fixer.py
index e939a823d1..781da4112f 100755
--- a/llm_toolkit/code_fixer.py
+++ b/llm_toolkit/code_fixer.py
@@ -29,6 +29,7 @@
 
 ERROR_LINES = 20
 NO_MEMBER_ERROR_REGEX = r"error: no member named '.*' in '([^':]*):?.*'"
+FILE_NOT_FOUND_ERROR_REGEX = r"fatal error: '([^']*)' file not found"
 
 
 def parse_args():
@@ -410,8 +411,10 @@ def apply_llm_fix(ai_binary: str,
   builder = prompt_builder.DefaultTemplateBuilder(fixer_model)
 
   context = _collect_context(benchmark, errors)
+  instruction = _collect_instructions(benchmark, errors,
+                                      fuzz_target_source_code)
   prompt = builder.build_fixer_prompt(benchmark, fuzz_target_source_code,
-                                      error_desc, errors, context)
+                                      error_desc, errors, context, instruction)
   prompt.save(prompt_path)
 
   fixer_model.generate_code(prompt, response_dir)
@@ -441,6 +444,69 @@ def _collect_context_no_member(benchmark: benchmarklib.Benchmark,
   return ci.get_type_def(target_type)
 
 
+def _collect_instructions(benchmark: benchmarklib.Benchmark, errors: list[str],
+                          fuzz_target_source_code: str) -> str:
+  """Collects the useful instructions to fix the errors."""
+  if not errors:
+    return ''
+
+  instruction = ''
+  for error in errors:
+    instruction += _collect_instruction_file_not_found(benchmark, error,
+                                                       fuzz_target_source_code)
+  return instruction
+
+
+def _collect_instruction_file_not_found(benchmark: benchmarklib.Benchmark,
+                                        error: str,
+                                        fuzz_target_source_code: str) -> str:
+  """Collects the useful instruction to fix 'file not found' errors."""
+  matched = re.search(FILE_NOT_FOUND_ERROR_REGEX, error)
+  if not matched:
+    return ''
+
+  # Step 1: Say the file does not exist, do not include it.
+  wrong_file = matched.group(1)
+  instruction = (
+      f'IMPORTANT: DO NOT include the header file {wrong_file} in the generated'
+      'fuzz target again, the file does not exist in the project-under-test.\n')
+
+  ci = context_introspector.ContextRetriever(benchmark)
+  # Step 2: Suggest the header/source file of the function under test.
+  function_file = ci.get_target_function_file_path()
+  if f'#include "{function_file}"' in fuzz_target_source_code:
+    function_file_base_name = os.path.basename(function_file)
+
+    instruction += (
+        'In the generated code, ensure that the path prefix of <code>'
+        f'{function_file_base_name}</code> is consistent with other include '
+        f'statements related to the project ({benchmark.project}). For example,'
+        'if another include statement is '
+        f'<code>#include <{benchmark.project}/header.h></code>, you must modify'
+        f' the path prefix in <code>#include "{function_file}"</code> to match '
+        'it, resulting in <code>'
+        f'#include <{benchmark.project}/{function_file_base_name}></code>.')
+    return instruction
+
+  if function_file:
+    instruction += (
+        f'If the non-existent <filepath>{wrong_file}</filepath> was included '
+        f'for the declaration of <code>{benchmark.function_signature}</code>, '
+        'you must replace it with the EXACT path of the actual file <filepath>'
+        f'{function_file}</filepath>. For example:\n'
+        f'<code>\n#include "{function_file}"\n</code>\n')
+
+  # Step 2: Suggest similar alternatives.
+  similar_headers = ci.get_similar_header_file_paths(wrong_file)
+  if similar_headers:
+    statements = '\n'.join(
+        [f'#include "{header}"' for header in similar_headers])
+    instruction += (
+        'Otherwise, consider replacing it with some of the following statements'
+        f'that may be correct alternatives:\n<code>\n{statements}\n</code>\n')
+  return instruction
+
+
 def main():
   args = parse_args()
   fix_all_targets(args.target_dir, args.project)
diff --git a/llm_toolkit/prompt_builder.py b/llm_toolkit/prompt_builder.py
index ff33af2419..4f99023db7 100644
--- a/llm_toolkit/prompt_builder.py
+++ b/llm_toolkit/prompt_builder.py
@@ -139,6 +139,8 @@ def __init__(self,
         template_dir, 'fixer_problem.txt')
     self.fixer_context_template_file = self._find_template(
         template_dir, 'fixer_context.txt')
+    self.fixer_instruction_template_file = self._find_template(
+        template_dir, 'fixer_instruction.txt')
     self.triager_priming_template_file = self._find_template(
         template_dir, 'triager_priming.txt')
     self.triager_problem_template_file = self._find_template(
@@ -302,11 +304,12 @@ def build_fixer_prompt(self,
                          raw_code: str,
                          error_desc: Optional[str],
                          errors: list[str],
-                         context: str = '') -> prompts.Prompt:
+                         context: str = '',
+                         instruction: str = '') -> prompts.Prompt:
     """Prepares the code-fixing prompt."""
     priming, priming_weight = self._format_fixer_priming(benchmark)
     problem = self._format_fixer_problem(raw_code, error_desc, errors,
-                                         priming_weight, context)
+                                         priming_weight, context, instruction)
 
     self._prepare_prompt(priming, problem)
     return self._prompt
@@ -328,7 +331,7 @@ def _format_fixer_priming(self, benchmark: Benchmark) -> Tuple[str, int]:
 
   def _format_fixer_problem(self, raw_code: str, error_desc: Optional[str],
                             errors: list[str], priming_weight: int,
-                            context: str) -> str:
+                            context: str, instruction: str) -> str:
     """Formats a problem for code fixer based on the template."""
     with open(self.fixer_problem_template_file) as f:
       problem = f.read().strip()
@@ -346,6 +349,12 @@ def _format_fixer_problem(self, raw_code: str, error_desc: Optional[str],
       context = context_template.replace('{CONTEXT_SOURCE_CODE}', context)
     problem = problem.replace('{CONTEXT}', context)
 
+    if instruction:
+      with open(self.fixer_instruction_template_file) as f:
+        instruction_template = f.read().strip()
+      instruction = instruction_template.replace('{INSTRUCTION}', instruction)
+    problem = problem.replace('{INSTRUCTION}', instruction)
+
     problem_prompt = self._prompt.create_prompt_piece(problem, 'user')
     template_piece = self._prompt.create_prompt_piece('{ERROR_MESSAGES}',
                                                       'user')
diff --git a/prompts/template_xml/fixer_instruction.txt b/prompts/template_xml/fixer_instruction.txt
new file mode 100644
index 0000000000..a46da218df
--- /dev/null
+++ b/prompts/template_xml/fixer_instruction.txt
@@ -0,0 +1,4 @@
+Below are instructions to assist you in fixing the error.
+<instruction>
+{INSTRUCTION}
+</instruction>
diff --git a/prompts/template_xml/fixer_problem.txt b/prompts/template_xml/fixer_problem.txt
index e182afe1ee..8f91b6e2f5 100644
--- a/prompts/template_xml/fixer_problem.txt
+++ b/prompts/template_xml/fixer_problem.txt
@@ -10,6 +10,7 @@ Below is the error to fix:
 </error>
 
 {CONTEXT}
+{INSTRUCTION}
 
 Fix code:
 1. Consider possible solutions for the issues listed above.