diff --git a/docs/changelog.rst b/docs/changelog.rst
index 7b3e97b0..e6e3bcf4 100644
--- a/docs/changelog.rst
+++ b/docs/changelog.rst
@@ -48,6 +48,8 @@ v0.20.0 (UNRELEASED)
   This can be used to show absolutely all log records, including those at
   custom levels below ``DEBUG``.
 
+- Add debug logging of unknown sections. (Fixes: :issue:`694`)
+
 **Logging**
 
 - Add custom log level ``TRACE`` (numerical level 5), which can be used by
diff --git a/mopidy/config/__init__.py b/mopidy/config/__init__.py
index 7c4f8755..f6fd2709 100644
--- a/mopidy/config/__init__.py
+++ b/mopidy/config/__init__.py
@@ -177,13 +177,19 @@ def _validate(raw_config, schemas):
     # Get validated config
     config = {}
     errors = {}
+    sections = set(raw_config)
     for schema in schemas:
+        sections.discard(schema.name)
         values = raw_config.get(schema.name, {})
         result, error = schema.deserialize(values)
         if error:
             errors[schema.name] = error
         if result:
             config[schema.name] = result
+
+    for section in sections:
+        logger.debug('Ignoring unknown config section: %s', section)
+
     return config, errors