diff --git a/.github/workflows/dynamic_arch.yml b/.github/workflows/dynamic_arch.yml
index a4e6d2e0d..9d1990e60 100644
--- a/.github/workflows/dynamic_arch.yml
+++ b/.github/workflows/dynamic_arch.yml
@@ -269,6 +269,7 @@ jobs:
                 -DNUM_THREADS=64 \
                 -DTARGET=CORE2 \
                 -DCMAKE_Fortran_FLAGS_RELEASE=-O2 \
+                -DCMAKE_C_FLAGS_RELEASE=-O2 \
                 ${{ matrix.idx64-flags }} \
                 -DCMAKE_C_COMPILER_LAUNCHER=ccache \
                 -DCMAKE_Fortran_COMPILER_LAUNCHER=ccache \