diff --git a/src/one-body-sample.cc b/src/one-body-sample.cc
index db4fe8ec027c7e9142b78730022878906a044108..fd1f4bf0872def4baeef0f97358a7a3c25103f11 100644
--- a/src/one-body-sample.cc
+++ b/src/one-body-sample.cc
@@ -233,10 +233,10 @@ int main(int argc, char *argv[]) {
       b2 = b1;
       b3 = b1;
 
-      // b += linear update
-      stiffnessMatrix.umv(u1_diff_old, b1);
-      stiffnessMatrix.umv(u2_diff_old, b2);
-      stiffnessMatrix.umv(u3_diff_old, b3);
+      // b -= linear update
+      stiffnessMatrix.mmv(u1_diff_old, b1);
+      stiffnessMatrix.mmv(u2_diff_old, b2);
+      stiffnessMatrix.mmv(u3_diff_old, b3);
 
       // {{{ Assemble terms for the nonlinearity