diff --git a/qiskit_addon_sqd/fermion.py b/qiskit_addon_sqd/fermion.py
index 1c7f13b..afb4ce4 100644
--- a/qiskit_addon_sqd/fermion.py
+++ b/qiskit_addon_sqd/fermion.py
@@ -96,7 +96,6 @@ def solve_fermion(
     else:
         # This will become the default code path after the deprecation period.
         ci_strs = bitstring_matrix_to_ci_strs(bitstring_matrix, open_shell=open_shell)
-        ci_strs = ci_strs[::-1]
     ci_strs = _check_ci_strs(ci_strs)
 
     num_up = format(ci_strs[0][0], "b").count("1")
@@ -199,9 +198,7 @@ def optimize_orbitals(
         )
         ci_strs = bitstring_matrix
     else:
-        # Flip the output so the alpha CI strs are on the left with [::-1]
         ci_strs = bitstring_matrix_to_ci_strs(bitstring_matrix, open_shell=open_shell)
-        ci_strs = ci_strs[::-1]
     ci_strs = _check_ci_strs(ci_strs)
 
     num_up = format(ci_strs[0][0], "b").count("1")
diff --git a/releasenotes/notes/fermion-bug-2b2ed34f979b1321.yaml b/releasenotes/notes/fermion-bug-2b2ed34f979b1321.yaml
new file mode 100644
index 0000000..087972f
--- /dev/null
+++ b/releasenotes/notes/fermion-bug-2b2ed34f979b1321.yaml
@@ -0,0 +1,3 @@
+fixes:
+  - |
+    Fixes a bug in :func:`qiskit_addon_sqd.fermion.solve_fermion` and :func:`qiskit_addon_sqd.fermion.optimize_orbitals` which causes the determinants for spin-up and spin-down to be incorrectly flipped before solving.