diff --git a/src/engine/engine_util_solve.c b/src/engine/engine_util_solve.c
index f82055a1..b93022b6 100644
--- a/src/engine/engine_util_solve.c
+++ b/src/engine/engine_util_solve.c
@@ -708,7 +708,7 @@ void mju_solveLUSparse(mjtNum* res, const mjtNum* LU, const mjtNum* vec, int n,
 
 // eigenvalue decomposition of symmetric 3x3 matrix
 static const mjtNum eigEPS = 1E-12;
-int mju_eig3(mjtNum* eigval, mjtNum* eigvec, mjtNum quat[4], const mjtNum mat[9]) {
+int mju_eig3(mjtNum eigval[3], mjtNum eigvec[9], mjtNum quat[4], const mjtNum mat[9]) {
   mjtNum D[9], tmp[9];
   mjtNum tau, t, c;
   int iter, rk, ck, rotk;
diff --git a/src/engine/engine_util_solve.h b/src/engine/engine_util_solve.h
index 910e5743..a5cf8697 100644
--- a/src/engine/engine_util_solve.h
+++ b/src/engine/engine_util_solve.h
@@ -84,7 +84,7 @@ void mju_solveLUSparse(mjtNum *res, const mjtNum *LU, const mjtNum* vec, int n,
                        const int *rownnz, const int *rowadr, const int *colind);
 
 // eigenvalue decomposition of symmetric 3x3 matrix
-MJAPI int mju_eig3(mjtNum* eigval, mjtNum* eigvec, mjtNum quat[4], const mjtNum mat[9]);
+MJAPI int mju_eig3(mjtNum eigval[3], mjtNum eigvec[9], mjtNum quat[4], const mjtNum mat[9]);
 
 // solve QCQP in 2 dimensions:
 //  min  0.5*x'*A*x + x'*b  s.t.  sum (xi/di)^2 <= r^2