diff --git a/autotests/input/syntax/testlang.xml b/autotests/input/syntax/testlang.xml
new file mode 100644
--- /dev/null
+++ b/autotests/input/syntax/testlang.xml
@@ -0,0 +1,27 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<!DOCTYPE language SYSTEM "language.dtd">
+<language name="Test Syntax" section="Others" version="1" kateversion="5.0">
+  <highlighting>
+    <list name="keywords">
+      <item>one</item>
+      <item>two</item>
+      <item>three</item>
+    </list>
+
+    <contexts>
+      <context name="Normal" attribute="Normal Text" lineEndContext="#stay">
+        <DetectSpaces />
+        <keyword attribute="Keyword" context="#stay" String="keywords" />
+        <DetectIdentifier />
+      </context>
+    </contexts>
+
+    <itemDatas>
+      <itemData name="Normal Text" defStyleNum="dsNormal" />
+      <itemData name="Keyword"     defStyleNum="dsKeyword" spellChecking="false" />
+    </itemDatas>
+  </highlighting>
+  <general>
+    <keywords casesensitive="1" />
+  </general>
+</language>
diff --git a/autotests/input/themes/customtheme.theme b/autotests/input/themes/customtheme.theme
new file mode 100644
--- /dev/null
+++ b/autotests/input/themes/customtheme.theme
@@ -0,0 +1,46 @@
+{
+    "metadata" : {
+        "revision" : 1,
+        "name" : "Test Theme"
+    },
+    "text-styles": {
+        "Normal" : {
+            "text-color" : "#1f1c1b",
+            "selected-text-color" : "#ffffff",
+            "bold" : false,
+            "italic" : false,
+            "underline" : false,
+            "strike-through" : false
+        }
+    },
+    "editor-colors": {
+        "background-color" : "#ffffff",
+        "code-folding" : "#94caef",
+        "bracket-matching" : "#ffff00",
+        "current-line" : "#f8f7f6",
+        "icon-border" : "#f0f0f0",
+        "indentation-line" : "#d2d2d2",
+        "line-numbers" : "#a0a0a0",
+        "current-line-number" : "#1e1e1e",
+        "mark-bookmark" : "#0000ff",
+        "mark-breakpoint-active" : "#ff0000",
+        "mark-breakpoint-reached" : "#ffff00",
+        "mark-breakpoint-disabled" : "#ff00ff",
+        "mark-execution" : "#a0a0a4",
+        "mark-warning" : "#00ff00",
+        "mark-error" : "#ff0000",
+        "modified-lines" : "#fdbc4b",
+        "replace-highlight" : "#00ff00",
+        "saved-lines" : "#2ecc71",
+        "search-highlight" : "#ffff00",
+        "selection" : "#94caef",
+        "separator" : "#898887",
+        "spell-checking" : "#bf0303",
+        "tab-marker" : "#d2d2d2",
+        "template-background" : "#d6d2d0",
+        "template-placeholder" : "#baf8ce",
+        "template-focused-placeholder" : "#76da98",
+        "template-read-only-placeholder" : "#f6e6e6",
+        "word-wrap-marker" : "#ededed"
+    }
+}
diff --git a/autotests/syntaxrepository_test.cpp b/autotests/syntaxrepository_test.cpp
--- a/autotests/syntaxrepository_test.cpp
+++ b/autotests/syntaxrepository_test.cpp
@@ -15,6 +15,8 @@
     along with this program.  If not, see <http://www.gnu.org/licenses/>.
 */
 
+#include "test-config.h"
+
 #include <abstracthighlighter.h>
 #include <definition.h>
 #include <format.h>
@@ -177,6 +179,22 @@
         }
         hl.highlightLine(QLatin1String("/**! @todo this should not crash .*/"), State());
     }
+
+    void testCustomPath()
+    {
+        QString testInputPath = QStringLiteral(TESTSRCDIR "/input");
+
+        Repository repo;
+        QVERIFY(repo.customSearchPaths().empty());
+        repo.addCustomSearchPath(testInputPath);
+        QCOMPARE(repo.customSearchPaths().size(), 1);
+        QCOMPARE(repo.customSearchPaths()[0], testInputPath);
+
+        auto customDefinition = repo.definitionForName(QLatin1String("Test Syntax"));
+        QVERIFY(customDefinition.isValid());
+        auto customTheme = repo.theme(QLatin1String("Test Theme"));
+        QVERIFY(customTheme.isValid());
+    }
 };
 }
 
diff --git a/src/lib/repository.h b/src/lib/repository.h
--- a/src/lib/repository.h
+++ b/src/lib/repository.h
@@ -153,6 +153,20 @@
      */
     void reload();
 
+    /**
+     * Add a custom search path to the repository.
+     * This path will be searched in addition to the usual locations for
+     * syntax and theme definition files.
+     */
+    void addCustomSearchPath(const QString &path);
+
+    /**
+     * Returns the list of custom search paths added to the repository.
+     * By default, this list is empty.
+     * @see addCustomSearchPath()
+     */
+    QVector<QString> customSearchPaths() const;
+
 private:
     Q_DISABLE_COPY(Repository)
     friend class RepositoryPrivate;
diff --git a/src/lib/repository.cpp b/src/lib/repository.cpp
--- a/src/lib/repository.cpp
+++ b/src/lib/repository.cpp
@@ -138,6 +138,9 @@
 
     loadSyntaxFolder(repo, QStringLiteral(":/org.kde.syntax-highlighting/syntax"));
 
+    foreach (const auto &path, m_customSearchPaths)
+        loadSyntaxFolder(repo, path + QStringLiteral("/syntax"));
+
     m_sortedDefs.reserve(m_defs.size());
     for (auto it = m_defs.constBegin(); it != m_defs.constEnd(); ++it)
         m_sortedDefs.push_back(it.value());
@@ -153,6 +156,9 @@
     foreach (const auto &dir, dirs)
         loadThemeFolder(dir);
     loadThemeFolder(QStringLiteral(":/org.kde.syntax-highlighting/themes"));
+
+    foreach (const auto &path, m_customSearchPaths)
+        loadThemeFolder(path + QStringLiteral("/themes"));
 }
 
 void RepositoryPrivate::loadSyntaxFolder(Repository *repo, const QString &path)
@@ -266,3 +272,14 @@
 
     d->load(this);
 }
+
+void Repository::addCustomSearchPath(const QString &path)
+{
+    d->m_customSearchPaths.append(path);
+    reload();
+}
+
+QVector<QString> Repository::customSearchPaths() const
+{
+    return d->m_customSearchPaths;
+}
diff --git a/src/lib/repository_p.h b/src/lib/repository_p.h
--- a/src/lib/repository_p.h
+++ b/src/lib/repository_p.h
@@ -47,6 +47,8 @@
     quint16 foldingRegionId(const QString &defName, const QString &foldName);
     quint16 nextFormatId();
 
+    QVector<QString> m_customSearchPaths;
+
     QHash<QString, Definition> m_defs;
     QVector<Definition> m_sortedDefs;