diff --git a/Eigen/src/Geometry/Quaternion.h b/Eigen/src/Geometry/Quaternion.h
index 19276b96a..56fa2bfbf 100644
--- a/Eigen/src/Geometry/Quaternion.h
+++ b/Eigen/src/Geometry/Quaternion.h
@@ -278,6 +278,10 @@ public:
   inline const Coefficients& coeffs() const { return m_coeffs;}
 
   EIGEN_MAKE_ALIGNED_OPERATOR_NEW_IF(NeedsAlignment)
+  
+#ifdef EIGEN_QUATERNION_PLUGIN
+# include EIGEN_QUATERNION_PLUGIN
+#endif
 
 protected:
   Coefficients m_coeffs;
diff --git a/doc/PreprocessorDirectives.dox b/doc/PreprocessorDirectives.dox
index 6ffa2fc26..76ce2eb99 100644
--- a/doc/PreprocessorDirectives.dox
+++ b/doc/PreprocessorDirectives.dox
@@ -106,6 +106,7 @@ following macros are supported; none of them are defined by default.
  - \b EIGEN_MATRIX_PLUGIN - filename of plugin for extending the Matrix class.
  - \b EIGEN_MATRIXBASE_PLUGIN - filename of plugin for extending the MatrixBase class.
  - \b EIGEN_PLAINOBJECTBASE_PLUGIN - filename of plugin for extending the PlainObjectBase class.
+ - \b EIGEN_QUATERNION_PLUGIN - filename of plugin for extending the Quaternion class.
  - \b EIGEN_QUATERNIONBASE_PLUGIN - filename of plugin for extending the QuaternionBase class.
  - \b EIGEN_SPARSEMATRIX_PLUGIN - filename of plugin for extending the SparseMatrix class.
  - \b EIGEN_SPARSEMATRIXBASE_PLUGIN - filename of plugin for extending the SparseMatrixBase class.