diff --git a/src/cpu/rv32cpu.c b/src/cpu/rv32cpu.c
index 1028e6a..bea9c9c 100644
--- a/src/cpu/rv32cpu.c
+++ b/src/cpu/rv32cpu.c
@@ -570,7 +570,9 @@ static void cpu_execute(rv32_cpu_t* cpu, instruction_t* instruction)
 					cpu->regs.x[instruction->rd] = csrrwi_old_value;
 					break;
 				case FUNC3_CSRRSI:
-					fprintf(stderr, "CSRRSI\n");
+					// CSR atomic Read and Set bits immediate
+					cpu->regs.x[instruction->rd] = cpu->csr[instruction->immediate];
+					cpu->csr[instruction->immediate] |= instruction->rs1;
 					break;
 				case FUNC3_CSRRCI:
 					// CSR atomic Read and Clear bits Immediate (immediate in rs1)