diff --git a/src/mos6502.exec.c b/src/mos6502.exec.c
index bb09cfe..aba595e 100644
--- a/src/mos6502.exec.c
+++ b/src/mos6502.exec.c
@@ -32,6 +32,7 @@ DEFINE_INST(brk)
     mos6502_push_stack(cpu, cpu->PC & 0xff);
     mos6502_push_stack(cpu, cpu->P);
     cpu->P |= MOS_INTERRUPT;
+    cpu->P &= ~MOS_DECIMAL;
     cpu->PC += 2;
 }
 
diff --git a/tests/mos6502.exec.c b/tests/mos6502.exec.c
index a88c0cc..72419f1 100644
--- a/tests/mos6502.exec.c
+++ b/tests/mos6502.exec.c
@@ -8,12 +8,18 @@ TestSuite(mos6502_exec, .init = setup, .fini = teardown);
 
 Test(mos6502_exec, brk)
 {
+    // Start out with the decimal bit high so we can test it gets turned
+    // off; this assignment also guarantees the I bit is low, and that
+    // should be set high by the handler as well.
+    cpu->P = MOS_DECIMAL;
+
     vm_8bit orig_P = cpu->P;
 
     cpu->PC = 123;
     mos6502_handle_brk(cpu, 0);
     cr_assert_eq(cpu->PC, 125);
     cr_assert_eq(cpu->P & MOS_INTERRUPT, MOS_INTERRUPT);
+    cr_assert_eq(cpu->P & MOS_DECIMAL, 0);
 
     cr_assert_eq(mos6502_pop_stack(cpu), orig_P);
     cr_assert_eq(mos6502_pop_stack(cpu), 123);