diff --git a/src/cmdline.c b/src/cmdline.c
index 9b393ab..cfdd8c1 100644
--- a/src/cmdline.c
+++ b/src/cmdline.c
@@ -327,7 +327,7 @@ static int killblank(opt_t *result, char *optarg)
             result->killblank = 0;
         }
         else {
-            fprintf(stderr, "%s: -k: invalid parameter\n", PROJECT);
+            bx_fprintf(stderr, "%s: -k: invalid parameter\n", PROJECT);
             return 1;
         }
     }
diff --git a/utest/cmdline_test.c b/utest/cmdline_test.c
index 7d10a01..3e26f03 100644
--- a/utest/cmdline_test.c
+++ b/utest/cmdline_test.c
@@ -118,4 +118,49 @@ void test_indentmode_text(void **state)
 }
 
 
+void test_killblank_true(void **state)
+{
+    (void) state;  /* unused */
+
+    opt_t *actual = act(2, "-k", "true");
+
+    assert_non_null(actual);
+    assert_int_equal(1, (int) actual->killblank);
+}
+
+
+void test_killblank_false(void **state)
+{
+    (void) state;  /* unused */
+
+    opt_t *actual = act(2, "-k", "false");
+
+    assert_non_null(actual);
+    assert_int_equal(0, (int) actual->killblank);
+}
+
+
+void test_killblank_invalid(void **state)
+{
+    (void) state;  /* unused */
+
+    opt_t *actual = act(2, "-k", "INVALID");
+
+    assert_null(actual);   // invalid option, so we would need to exit with error
+    assert_int_equal(1, collect_err_size);
+    assert_string_equal("boxes: -k: invalid parameter\n", collect_err[0]);
+}
+
+
+void test_killblank_multiple(void **state)
+{
+    (void) state;  /* unused */
+
+    opt_t *actual = act(4, "-k", "true", "-k", "false");    // first one wins
+
+    assert_non_null(actual);
+    assert_int_equal(1, (int) actual->killblank);
+}
+
+
 /*EOF*/                                          /* vim: set cindent sw=4: */
diff --git a/utest/cmdline_test.h b/utest/cmdline_test.h
index 060e59e..b754e8b 100644
--- a/utest/cmdline_test.h
+++ b/utest/cmdline_test.h
@@ -32,6 +32,11 @@ void test_indentmode_invalid_short(void **state);
 void test_indentmode_box(void **state);
 void test_indentmode_text(void **state);
 
+void test_killblank_true(void **state);
+void test_killblank_false(void **state);
+void test_killblank_invalid(void **state);
+void test_killblank_multiple(void **state);
+
 
 #endif
 
diff --git a/utest/main.c b/utest/main.c
index c603441..5cfd0c5 100644
--- a/utest/main.c
+++ b/utest/main.c
@@ -52,7 +52,11 @@ int main(void)
         cmocka_unit_test_setup(test_indentmode_invalid_long, beforeTest),
         cmocka_unit_test_setup(test_indentmode_invalid_short, beforeTest),
         cmocka_unit_test_setup(test_indentmode_box, beforeTest),
-        cmocka_unit_test_setup(test_indentmode_text, beforeTest)
+        cmocka_unit_test_setup(test_indentmode_text, beforeTest),
+        cmocka_unit_test_setup(test_killblank_true, beforeTest),
+        cmocka_unit_test_setup(test_killblank_false, beforeTest),
+        cmocka_unit_test_setup(test_killblank_invalid, beforeTest),
+        cmocka_unit_test_setup(test_killblank_multiple, beforeTest)
     };
 
     const struct CMUnitTest regulex_tests[] = {