diff --git a/lib/addoninfo.cpp b/lib/addoninfo.cpp
index c0139320d7e..388484916ea 100644
--- a/lib/addoninfo.cpp
+++ b/lib/addoninfo.cpp
@@ -39,24 +39,36 @@ static std::string getFullPath(const std::string &fileName, const std::string &e
         return "";
 
     const std::string exepath = Path::getPathFromFilename(exename);
-    if (debug)
-        std::cout << "looking for addon '" << (exepath + fileName) << "'" << std::endl;
-    if (Path::isFile(exepath + fileName))
-        return exepath + fileName;
-    if (debug)
-        std::cout << "looking for addon '" << (exepath + "addons/" + fileName) << "'" << std::endl;
-    if (Path::isFile(exepath + "addons/" + fileName))
-        return exepath + "addons/" + fileName;
+    {
+        std::string p = Path::join(exepath, fileName);
+        if (debug)
+            std::cout << "looking for addon '" << p << "'" << std::endl;
+        if (Path::isFile(p))
+            return p;
+    }
+    {
+        std::string p = Path::join(exepath, "addons", fileName);
+        if (debug)
+            std::cout << "looking for addon '" << p << "'" << std::endl;
+        if (Path::isFile(p))
+            return p;
+    }
 
 #ifdef FILESDIR
-    if (debug)
-        std::cout << "looking for addon '" << (FILESDIR + ("/" + fileName)) << "'" << std::endl;
-    if (Path::isFile(FILESDIR + ("/" + fileName)))
-        return FILESDIR + ("/" + fileName);
-    if (debug)
-        std::cout << "looking for addon '" << (FILESDIR + ("/addons/" + fileName)) << "'" << std::endl;
-    if (Path::isFile(FILESDIR + ("/addons/" + fileName)))
-        return FILESDIR + ("/addons/" + fileName);
+    {
+        std::string p = Path::join(FILESDIR, fileName);
+        if (debug)
+            std::cout << "looking for addon '" << p << "'" << std::endl;
+        if (Path::isFile(p))
+            return p;
+    }
+    {
+        std::string p = Path::join(FILESDIR, "addons", fileName);
+        if (debug)
+            std::cout << "looking for addon '" << p << "'" << std::endl;
+        if (Path::isFile(p))
+            return p;
+    }
 #endif
     return "";
 }
diff --git a/lib/path.cpp b/lib/path.cpp
index 0e6e5e8ae9c..d679f3beceb 100644
--- a/lib/path.cpp
+++ b/lib/path.cpp
@@ -458,3 +458,8 @@ std::string Path::join(std::string path1, std::string path2)
         return path2;
     return ((path1.back() == '/') ? path1 : (path1 + "/")) + path2;
 }
+
+std::string Path::join(std::string path1, std::string path2, std::string path3)
+{
+    return Path::join(Path::join(std::move(path1), std::move(path2)), std::move(path3));
+}
diff --git a/lib/path.h b/lib/path.h
index 23db06c4e50..fcc46b48b5b 100644
--- a/lib/path.h
+++ b/lib/path.h
@@ -206,6 +206,13 @@ class CPPCHECKLIB Path {
      * @return the joined path with normalized slashes
      */
     static std::string join(std::string path1, std::string path2);
+
+    /**
+     * @brief join 3 paths with '/' separators
+     * if path2 is an absolute path path1 will be dismissed.
+     * @return the joined path with normalized slashes
+     */
+    static std::string join(std::string path1, std::string path2, std::string path3);
 };
 
 /// @}
diff --git a/test/cli/lookup_test.py b/test/cli/lookup_test.py
index cab96a7f6bb..f8c9c8e65ec 100644
--- a/test/cli/lookup_test.py
+++ b/test/cli/lookup_test.py
@@ -644,12 +644,14 @@ def test_addon_lookup(tmpdir):
     exitcode, stdout, stderr, exe = cppcheck_ex(['--debug-lookup=addon', '--addon=misra', test_file])
     exepath = os.path.dirname(exe)
     exepath_sep = exepath + os.path.sep
+    if sys.platform == 'win32':
+        exepath_sep = exepath_sep.replace('\\', '/')
     assert exitcode == 0, stdout if stdout else stderr
     lines = stdout.splitlines()
     assert lines == [
         "looking for addon 'misra.py'",
         "looking for addon '{}misra.py'".format(exepath_sep),
-        "looking for addon '{}addons/misra.py'".format(exepath_sep),  # TODO: mixed separators
+        "looking for addon '{}addons/misra.py'".format(exepath_sep),
         'Checking {} ...'.format(test_file)
     ]
 
@@ -662,12 +664,14 @@ def test_addon_lookup_ext(tmpdir):
     exitcode, stdout, stderr, exe = cppcheck_ex(['--debug-lookup=addon', '--addon=misra.py', test_file])
     exepath = os.path.dirname(exe)
     exepath_sep = exepath + os.path.sep
+    if sys.platform == 'win32':
+        exepath_sep = exepath_sep.replace('\\', '/')
     assert exitcode == 0, stdout if stdout else stderr
     lines = stdout.splitlines()
     assert lines == [
         "looking for addon 'misra.py'",
         "looking for addon '{}misra.py'".format(exepath_sep),
-        "looking for addon '{}addons/misra.py'".format(exepath_sep),  # TODO: mixed separators
+        "looking for addon '{}addons/misra.py'".format(exepath_sep),
         'Checking {} ...'.format(test_file)
     ]
 
@@ -680,12 +684,14 @@ def test_addon_lookup_notfound(tmpdir):
     exitcode, stdout, _, exe = cppcheck_ex(['--debug-lookup=addon', '--addon=none', test_file])
     exepath = os.path.dirname(exe)
     exepath_sep = exepath + os.path.sep
+    if sys.platform == 'win32':
+        exepath_sep = exepath_sep.replace('\\', '/')
     assert exitcode == 1, stdout
     lines = stdout.splitlines()
     assert lines == [
         "looking for addon 'none.py'",
         "looking for addon '{}none.py'".format(exepath_sep),
-        "looking for addon '{}addons/none.py'".format(exepath_sep),  # TODO: mixed separators
+        "looking for addon '{}addons/none.py'".format(exepath_sep),
         'Did not find addon none.py'
     ]
 
@@ -696,13 +702,15 @@ def test_addon_lookup_notfound_project(tmpdir):  # #13940 / #13941
     exitcode, stdout, _, exe = cppcheck_ex(['--debug-lookup=addon', '--addon=none', '--project={}'.format(project_file)])
     exepath = os.path.dirname(exe)
     exepath_sep = exepath + os.path.sep
+    if sys.platform == 'win32':
+        exepath_sep = exepath_sep.replace('\\', '/')
     assert exitcode == 1, stdout
     lines = stdout.splitlines()
     assert lines == [
         # TODO: needs to look relative to the project file first
         "looking for addon 'none.py'",
         "looking for addon '{}none.py'".format(exepath_sep),
-        "looking for addon '{}addons/none.py'".format(exepath_sep),  # TODO: mixed separators
+        "looking for addon '{}addons/none.py'".format(exepath_sep),
         'Did not find addon none.py'
     ]
 
@@ -713,12 +721,14 @@ def test_addon_lookup_notfound_compdb(tmpdir):
     exitcode, stdout, _, exe = cppcheck_ex(['--debug-lookup=addon', '--addon=none', '--project={}'.format(compdb_file)])
     exepath = os.path.dirname(exe)
     exepath_sep = exepath + os.path.sep
+    if sys.platform == 'win32':
+        exepath_sep = exepath_sep.replace('\\', '/')
     assert exitcode == 1, stdout
     lines = stdout.splitlines()
     assert lines == [
         "looking for addon 'none.py'",
         "looking for addon '{}none.py'".format(exepath_sep),
-        "looking for addon '{}addons/none.py'".format(exepath_sep),  # TODO: mixed separators
+        "looking for addon '{}addons/none.py'".format(exepath_sep),
         'Did not find addon none.py'
     ]
 
@@ -731,12 +741,14 @@ def test_addon_lookup_ext_notfound(tmpdir):
     exitcode, stdout, _, exe = cppcheck_ex(['--debug-lookup=addon', '--addon=none.py', test_file])
     exepath = os.path.dirname(exe)
     exepath_sep = exepath + os.path.sep
+    if sys.platform == 'win32':
+        exepath_sep = exepath_sep.replace('\\', '/')
     assert exitcode == 1, stdout
     lines = stdout.splitlines()
     assert lines == [
         "looking for addon 'none.py'",
         "looking for addon '{}none.py'".format(exepath_sep),
-        "looking for addon '{}addons/none.py'".format(exepath_sep),  # TODO: mixed separators
+        "looking for addon '{}addons/none.py'".format(exepath_sep),
         'Did not find addon none.py'
     ]
 
@@ -749,12 +761,14 @@ def test_addon_lookup_relative_notfound(tmpdir):
     exitcode, stdout, _, exe = cppcheck_ex(['--debug-lookup=addon', '--addon=addon/misra.py', test_file])
     exepath = os.path.dirname(exe)
     exepath_sep = exepath + os.path.sep
+    if sys.platform == 'win32':
+        exepath_sep = exepath_sep.replace('\\', '/')
     assert exitcode == 1, stdout
     lines = stdout.splitlines()
     assert lines == [
         "looking for addon 'addon/misra.py'",
         "looking for addon '{}addon/misra.py'".format(exepath_sep),
-        "looking for addon '{}addons/addon/misra.py'".format(exepath_sep),  # TODO: mixed separators
+        "looking for addon '{}addons/addon/misra.py'".format(exepath_sep),
         'Did not find addon addon/misra.py'
     ]
 
@@ -767,12 +781,14 @@ def test_addon_lookup_relative_noext_notfound(tmpdir):
     exitcode, stdout, _, exe = cppcheck_ex(['--debug-lookup=addon', '--addon=addon/misra', test_file])
     exepath = os.path.dirname(exe)
     exepath_sep = exepath + os.path.sep
+    if sys.platform == 'win32':
+        exepath_sep = exepath_sep.replace('\\', '/')
     assert exitcode == 1, stdout
     lines = stdout.splitlines()
     assert lines == [
         "looking for addon 'addon/misra.py'",
         "looking for addon '{}addon/misra.py'".format(exepath_sep),
-        "looking for addon '{}addons/addon/misra.py'".format(exepath_sep),  # TODO: mixed separators
+        "looking for addon '{}addons/addon/misra.py'".format(exepath_sep),
         'Did not find addon addon/misra.py'
     ]
 
@@ -825,12 +841,14 @@ def test_addon_lookup_nofile(tmpdir):
     exitcode, stdout, stderr, exe = cppcheck_ex(['--debug-lookup=addon', '--addon=misra', test_file])
     exepath = os.path.dirname(exe)
     exepath_sep = exepath + os.path.sep
+    if sys.platform == 'win32':
+        exepath_sep = exepath_sep.replace('\\', '/')
     assert exitcode == 0, stdout if stdout else stderr
     lines = stdout.splitlines()
     assert lines == [
         "looking for addon 'misra.py'",
         "looking for addon '{}misra.py'".format(exepath_sep),
-        "looking for addon '{}addons/misra.py'".format(exepath_sep),  # TODO: mixed separators
+        "looking for addon '{}addons/misra.py'".format(exepath_sep),
         'Checking {} ...'.format(test_file)
     ]
 
diff --git a/test/testpath.cpp b/test/testpath.cpp
index 44dea302762..f48a2fe53ab 100644
--- a/test/testpath.cpp
+++ b/test/testpath.cpp
@@ -202,6 +202,8 @@ class TestPath : public TestFixture {
         //ASSERT_EQUALS("", Path::join("S:/a", "S:/b"));
         //ASSERT_EQUALS("", Path::join("S:/a", "S:\\b"));
         //ASSERT_EQUALS("", Path::join("S:/a", "/b"));
+
+        ASSERT_EQUALS("a/b/c", Path::join("a", "b", "c"));
     }
 
     void isDirectory() const {