diff --git a/qmb/_hamiltonian_cuda.cu b/qmb/_hamiltonian_cuda.cu
index 3f3f88c..c54647d 100644
--- a/qmb/_hamiltonian_cuda.cu
+++ b/qmb/_hamiltonian_cuda.cu
@@ -42,7 +42,7 @@ __device__ bool get_bit(std::uint8_t* data, std::uint8_t index) {
     return ((*data) >> index) & 1;
 }
 
-__device__ bool set_bit(std::uint8_t* data, std::uint8_t index, bool value) {
+__device__ void set_bit(std::uint8_t* data, std::uint8_t index, bool value) {
     if (value) {
         *data |= (1 << index);
     } else {