diff --git a/doc/APIreference/functions.rst b/doc/APIreference/functions.rst
index 6bf64e11..04d8802a 100644
--- a/doc/APIreference/functions.rst
+++ b/doc/APIreference/functions.rst
@@ -2985,7 +2985,7 @@ mju_eig3
 
 .. mujoco-include:: mju_eig3
 
-Eigenvalue decomposition of symmetric 3x3 matrix.
+Eigenvalue decomposition of symmetric 3x3 matrix, mat = eigvec * diag(eigval) * eigvec'.
 
 .. _mju_boxQP:
 
diff --git a/include/mujoco/mujoco.h b/include/mujoco/mujoco.h
index 5ab8a363..cb6962a1 100644
--- a/include/mujoco/mujoco.h
+++ b/include/mujoco/mujoco.h
@@ -1118,7 +1118,7 @@ MJAPI void mju_bandMulMatVec(mjtNum* res, const mjtNum* mat, const mjtNum* vec,
 // Address of diagonal element i in band-dense matrix representation.
 MJAPI int mju_bandDiag(int i, int ntotal, int nband, int ndense);
 
-// Eigenvalue decomposition of symmetric 3x3 matrix.
+// Eigenvalue decomposition of symmetric 3x3 matrix, mat = eigvec * diag(eigval) * eigvec'.
 MJAPI int mju_eig3(mjtNum eigval[3], mjtNum eigvec[9], mjtNum quat[4], const mjtNum mat[9]);
 
 // minimize 0.5*x'*H*x + x'*g  s.t. lower <= x <= upper, return rank or -1 if failed
diff --git a/introspect/functions.py b/introspect/functions.py
index e57bd7a9..0e9d2568 100644
--- a/introspect/functions.py
+++ b/introspect/functions.py
@@ -7368,7 +7368,7 @@ FUNCTIONS: Mapping[str, FunctionDecl] = dict([
                  ),
              ),
          ),
-         doc='Eigenvalue decomposition of symmetric 3x3 matrix.',
+         doc="Eigenvalue decomposition of symmetric 3x3 matrix, mat = eigvec * diag(eigval) * eigvec'.",  # pylint: disable=line-too-long
      )),
     ('mju_boxQP',
      FunctionDecl(