diff --git a/StanHeaders/inst/include/libsundials b/StanHeaders/inst/include/libsundials
index f1525d058..6eac79798 120000
--- a/StanHeaders/inst/include/libsundials
+++ b/StanHeaders/inst/include/libsundials
@@ -1 +1 @@
-upstream/lib/stan_math/lib/sundials_5.6.1/
\ No newline at end of file
+upstream/lib/stan_math/lib/sundials_6.1.1/
\ No newline at end of file