diff --git a/docs/source/nnls_solving.rst b/docs/source/nnls_solving.rst
index 8267a51..c2d2369 100644
--- a/docs/source/nnls_solving.rst
+++ b/docs/source/nnls_solving.rst
@@ -513,7 +513,7 @@
 a :ref:`section-preconditioner` must be used to get reasonable
 performance. Currently only the ``JACOBI`` preconditioner is available
 for use with ``CGNR``. It uses the block diagonal of :math:`H` to
-preconditioner the normal equations.
+precondition the normal equations.
 
 When the user chooses ``CGNR`` as the linear solver, Ceres
 automatically switches from the exact step algorithm to an inexact