diff --git a/qutebrowser/config/config.py b/qutebrowser/config/config.py
index 7e74c16f0..036a9f068 100644
--- a/qutebrowser/config/config.py
+++ b/qutebrowser/config/config.py
@@ -240,8 +240,18 @@ class Config:
             The changed config part as string.
 
         """
-        # FIXME to be implemented
-        pass
+        lines = []
+        for secname, section in self.config.items():
+            changed_opts = []
+            for optname, option in section.items():
+                if (option.rawvalue is not None and
+                        option.rawvalue != option.default):
+                    keyval = '{} = {}'.format(optname, option)
+                    changed_opts.append(keyval)
+            if changed_opts:
+                lines.append('[{}]'.format(secname))
+                lines += changed_opts
+        return '\n'.join(lines)
 
     def optionxform(self, val):
         """Implemented to be compatible with ConfigParser interpolation."""
diff --git a/qutebrowser/config/conftypes.py b/qutebrowser/config/conftypes.py
index 6c45d14f5..e65cc4094 100644
--- a/qutebrowser/config/conftypes.py
+++ b/qutebrowser/config/conftypes.py
@@ -79,7 +79,7 @@ class SettingValue:
 
         """
         self.typ = typ()
-        self._rawvalue = None
+        self.rawvalue = None
         self.default = default
 
     def __str__(self):
@@ -94,12 +94,12 @@ class SettingValue:
     @property
     def value(self):
         """Get the currently valid value."""
-        return self._rawvalue if self._rawvalue is not None else self.default
+        return self.rawvalue if self.rawvalue is not None else self.default
 
     @value.setter
     def value(self, val):
         """Set the currently valid value."""
-        self._rawvalue = val
+        self.rawvalue = val
 
 
 class BaseType: