diff --git a/README.md b/README.md
index db84fbb..4486b8c 100644
--- a/README.md
+++ b/README.md
@@ -44,6 +44,10 @@ optional arguments:
   --trim, -t            Reduce continuous line breaks to one. Default: True
   --include_directory INCLUDE_DIRECTORY, -I INCLUDE_DIRECTORY
                         Add include directories for header files.
+  --source_directory SOURCE_DIRECTORY, -S SOURCE_DIRECTORY
+                        Set the source directories for source files.
+                        Use ./ in front of a path to mark as relative to the header file.
+
 ```
 
 ## Simple example
diff --git a/quom/__main__.py b/quom/__main__.py
index d717853..ed25d0b 100644
--- a/quom/__main__.py
+++ b/quom/__main__.py
@@ -1,12 +1,12 @@
 import argparse
 import sys
-import traceback
 from pathlib import Path
+from typing import List
 
 from .quom import Quom
 
 
-def main():
+def main(args: List[str]):
     parser = argparse.ArgumentParser(prog='quom', description='Single header generator for C/C++ libraries.')
     parser.add_argument('input_path', metavar='input', type=Path, help='Input file path of the main file.')
     parser.add_argument('output_path', metavar='output', type=Path,
@@ -20,12 +20,33 @@ def main():
                         help='Reduce continuous line breaks to one. Default: %(default)s')
     parser.add_argument('--include_directory', '-I', type=Path, action='append', default=[],
                         help='Add include directories for header files.')
+    parser.add_argument('--source_directory', '-S', type=str, action='append', default=['.'],
+                        help='Set the source directories for source files. '
+                             'Use ./ in front of a path to mark as relative to the header file.')
 
-    args = parser.parse_args()
+    args = parser.parse_args(args)
+
+    # Transform source directories to distingue between:
+    # - relative from header file (starting with dot)
+    # - relative from workdir
+    # - absolute path
+    relative_source_directories = []
+    source_directories = []
+    for src in args.source_directory:
+        path = Path(src)
+        if src == '.' or src.startswith('./'):
+            relative_source_directories.append(path)
+        else:
+            source_directories.append(path.resolve())
 
     with args.output_path.open('w+') as file:
-        Quom(args.input_path, file, args.stitch, args.include_guard, args.trim, args.include_directory)
+        Quom(args.input_path, file, args.stitch, args.include_guard, args.trim, args.include_directory,
+             relative_source_directories, source_directories)
+
+
+def run():
+    main(sys.argv[1:])
 
 
 if __name__ == '__main__':
-    sys.exit(main())
+    run()
diff --git a/quom/quom.py b/quom/quom.py
index 20bc83e..d366219 100644
--- a/quom/quom.py
+++ b/quom/quom.py
@@ -1,3 +1,4 @@
+import os
 import re
 from pathlib import Path
 from queue import Queue
@@ -29,12 +30,17 @@ def contains_only_whitespace_and_comment_tokens(tokens: List[Token]):
 class Quom:
     def __init__(self, src_file_path: Union[Path, str], dst: TextIO, stitch_format: str = None,
                  include_guard_format: str = None, trim: bool = True,
-                 include_directories: List[Union[Path, str]] = None):
+                 include_directories: List[Union[Path, str]] = None,
+                 relative_source_directories: List[Union[Path]] = None,
+                 source_directories: List[Union[Path]] = None):
         self.__dst = dst
         self.__stitch_format = stitch_format
         self.__include_guard_format = re.compile('^{}$'.format(include_guard_format)) if include_guard_format else None
         self.__trim = trim
         self.__include_directories = [Path(x) for x in include_directories] if include_directories else []
+        self.__relative_source_directories = relative_source_directories if relative_source_directories else [] \
+            if source_directories else [Path('.')]
+        self.__source_directories = source_directories if source_directories else [Path('.')]
 
         self.__processed_files = set()
         self.__source_files = Queue()
@@ -87,7 +93,9 @@ class Quom:
 
             self.__write_token(token, is_main_header)
 
-        self.__find_possible_source_file(file_path)
+        file_path = self.__find_possible_source_file(file_path)
+        if file_path:
+            self.__source_files.put(file_path)
 
     def __write_token(self, token: Token, is_main_header: bool):
         if isinstance(token, StartToken) or isinstance(token, EndToken):
@@ -129,16 +137,21 @@ class Quom:
                     contains_only_whitespace_and_comment_tokens(token.preprocessor_arguments[i + 1:]):
                 return True
 
-    def __find_possible_source_file(self, header_file_path: Path):
+    def __find_possible_source_file(self, header_file_path: Path) -> Union[Path, None]:
         if header_file_path.suffix in ['.c', '.cpp', '.cxx', '.cc', '.c++', '.cp', '.C']:
             return
 
         # Checks if a equivalent compilation unit exits.
         for extension in ['.c', '.cpp', '.cxx', '.cc', '.c++', '.cp', '.C']:
-            file_path = header_file_path.with_suffix(extension)
-            if file_path.exists():
-                self.__source_files.put(file_path)
-                break
+            for src_dir in self.__relative_source_directories:
+                file_path = (header_file_path.parent / src_dir / header_file_path.name).with_suffix(extension)
+                if file_path.exists():
+                    return file_path
+            for src_dir in self.__source_directories:
+                file_path = (src_dir / header_file_path.name).with_suffix(extension).resolve()
+                if file_path.exists():
+                    return file_path
+        return None
 
     def __scan_for_include(self, file_path: Path, token: Token, is_source_file: bool) -> Union[Token, None]:
         if not isinstance(token, PreprocessorIncludeToken) or not token.is_local_include:

diff --git a/tests/test_quom/test_normal.py b/tests/test_quom/test_normal.py
index f0928dd..38d53f0 100644
--- a/tests/test_quom/test_normal.py
+++ b/tests/test_quom/test_normal.py
@@ -4,6 +4,7 @@ from pathlib import Path
 import pytest
 
 from quom import Quom, QuomError
+from quom.__main__ import main
 
 FILE_MAIN_HPP = """\
 #pragma once
@@ -247,3 +248,13 @@ def test_with_missing_source_file(fs):
     Quom(Path('main.hpp'), dst)
 
     assert dst.getvalue() == RESULT_NORMAL_WITHOUT_SOURCES
+
+
+def test_main(fs):
+    init()
+
+    main(['main.hpp', 'result.hpp'])
+    assert Path('result.hpp').read_text() == RESULT_NORMAL
+
+    main(['main.hpp', 'result.hpp', '-S', '.'])
+    assert Path('result.hpp').read_text() == RESULT_NORMAL
diff --git a/tests/test_quom/test_source_directory.py b/tests/test_quom/test_source_directory.py
new file mode 100644
index 0000000..790d417
--- /dev/null
+++ b/tests/test_quom/test_source_directory.py
@@ -0,0 +1,62 @@
+import os
+from io import StringIO
+from pathlib import Path
+
+from quom import Quom
+from quom.__main__ import main
+
+FILE_MAIN_HPP = """
+int foo = 3;
+
+int foo();
+"""
+
+FILE_MAIN_CPP = """
+int foo() { return 42; }
+"""
+
+RESULT = """
+int foo = 3;
+
+int foo();
+
+int foo() { return 42; }
+"""
+
+
+def test_source_directory(fs):
+    os.makedirs('project/')
+    os.chdir('project/')
+    os.makedirs('include/')
+    os.makedirs('src/')
+
+    with open('include/main.hpp', 'w+') as file:
+        file.write(FILE_MAIN_HPP)
+
+    with open('src/main.cpp', 'w+') as file:
+        file.write(FILE_MAIN_CPP)
+
+    dst = StringIO()
+    Quom(Path('include/main.hpp'), dst)
+    assert dst.getvalue() != RESULT
+
+    dst = StringIO()
+    Quom(Path('include/main.hpp'), dst, relative_source_directories=[Path('../src')])
+    assert dst.getvalue() == RESULT
+
+    dst = StringIO()
+    Quom(Path('include/main.hpp'), dst, source_directories=[Path('src').resolve()])
+    assert dst.getvalue() == RESULT
+
+    dst = StringIO()
+    Quom(Path('include/main.hpp'), dst, source_directories=[Path('/project/src')])
+    assert dst.getvalue() == RESULT
+
+    main(['include/main.hpp', 'result.hpp', '-S', './../src'])
+    assert Path('result.hpp').read_text() == RESULT
+
+    main(['include/main.hpp', 'result.hpp', '-S', 'src'])
+    assert Path('result.hpp').read_text() == RESULT
+
+    main(['include/main.hpp', 'result.hpp', '-S', '/project/src'])
+    assert Path('result.hpp').read_text() == RESULT

Feature request - Additional directories to search for sources
Hi, I found this package very useful, but when trying to use it - encounter with a small problem. The case when sources are located in different directory then their headers - are not supported. The common folder structure of any project can be as follows:
_project/_
&nbsp;&nbsp;&nbsp;_public/_
&nbsp;&nbsp;&nbsp;_include/_
&nbsp;&nbsp;&nbsp;_src/_
So it would be nice if it will be possible to specify source directories relative to include directories. For instance via `--relative_source_dir` or `-SI` argument.
The most common use can be: `-SI "./" -SI "../" -SI "../src"`
By default the directory suffixes array is ["./'] but if at least one -SI argument provided it should be overwritten.
tests/test_quom/test_normal.py::test_main tests/test_quom/test_source_directory.py::test_source_directory
tests/test_quom/test_normal.py::test_with_missing_source_file tests/test_quom/test_normal.py::test_with_include_guard_format tests/test_quom/test_normal.py::test_with_mismatching_include_guard_format tests/test_quom/test_normal.py::test_normal tests/test_quom/test_normal.py::test_normal_without_trim tests/test_quom/test_normal.py::test_with_mismatching_stitch tests/test_quom/test_normal.py::test_with_stitch_location tests/test_quom/test_normal.py::test_with_missing_header_file