diff --git a/libraries/AP_Common/tests/test_bitmask.cpp b/libraries/AP_Common/tests/test_bitmask.cpp
index 49d2f57cf52f43..2a19431ea030af 100644
--- a/libraries/AP_Common/tests/test_bitmask.cpp
+++ b/libraries/AP_Common/tests/test_bitmask.cpp
@@ -53,6 +53,12 @@ void bitmask_tests(void)
     EXPECT_EXIT(x.set(N+1), testing::KilledBySignal(SIGABRT), "AP_InternalError::error_t::bitmask_range");
 #endif
 
+#if CONFIG_HAL_BOARD == HAL_BOARD_LINUX
+    x.clear(N+1);
+#elif CONFIG_HAL_BOARD == HAL_BOARD_SITL
+    EXPECT_EXIT(x.clear(N+1), testing::KilledBySignal(SIGABRT), "AP_InternalError::error_t::bitmask_range");
+#endif
+
     for (uint8_t i=0; i<N; i++) {
         EXPECT_EQ(x2.get(i), x.get(i));
     }
@@ -81,8 +87,10 @@ void bitmask_setall(void)
     Bitmask<N> x;
     EXPECT_EQ(-1, x.first_set());
     EXPECT_EQ(false, x.get(N-4));
+    EXPECT_EQ(0, x.count());
     x.setall();
     EXPECT_EQ(0, x.first_set());
+    EXPECT_EQ(N, x.count());
     x.clear(0);
     EXPECT_EQ(1, x.first_set());
     x.clear(1);
@@ -93,6 +101,7 @@ void bitmask_setall(void)
     EXPECT_EQ(-1, x.first_set());
     EXPECT_EQ(false, x.get(N-4));
     EXPECT_EQ(true, x.empty());
+    EXPECT_EQ(0, x.count());
 }
 
 TEST(Bitmask, SetAll31) { bitmask_setall<31>(); }
@@ -116,6 +125,7 @@ void bitmask_assignment(void)
 
     Bitmask<N> y;
     y = x;
+    EXPECT_EQ(true, x == y);
     x.clear(0);
     EXPECT_EQ(true, y.get(0));
     EXPECT_EQ(true, y.get(5));