diff --git a/power_manager/common/power_constants.h b/power_manager/common/power_constants.h
index 3b619ae..3a61084 100644
--- a/power_manager/common/power_constants.h
+++ b/power_manager/common/power_constants.h
@@ -46,7 +46,8 @@
 extern const char kRetrySuspendAttemptsPref[];
 
 // Minimum brightness level (in hardware-specific units) that the backlight
-// should be remain at before it's turned off entirely.
+// should be remain at before it's turned off entirely. If unset, a default
+// based on the maximum brightness level is used.
 extern const char kMinVisibleBacklightLevelPref[];
 
 // If true, powerd will jump directly from the min-visible-level to 0 rather
diff --git a/power_manager/default_prefs/min_visible_backlight_level b/power_manager/default_prefs/min_visible_backlight_level
deleted file mode 100644
index d00491f..0000000
--- a/power_manager/default_prefs/min_visible_backlight_level
+++ /dev/null
@@ -1 +0,0 @@
-1
diff --git a/power_manager/powerd/policy/internal_backlight_controller.cc b/power_manager/powerd/policy/internal_backlight_controller.cc
index 41005ab..a0390bc 100644
--- a/power_manager/powerd/policy/internal_backlight_controller.cc
+++ b/power_manager/powerd/policy/internal_backlight_controller.cc
@@ -38,15 +38,6 @@
 // kDefaultLevelToPercentExponent is modified.
 const double kDimmedBrightnessFraction = 0.1;
 
-// Minimum brightness, as a fraction of the maximum level in the range [0.0,
-// 1.0], that we'll remain at before turning the backlight off entirely.  This
-// is arbitrarily chosen but seems to be a reasonable marginally-visible
-// brightness for a darkened room on current devices: http://crosbug.com/24569.
-// A higher level can be set via the kMinVisibleBacklightLevelPref setting.
-// This is a fraction rather than a percent so it won't change if
-// kDefaultLevelToPercentExponent is modified.
-const double kDefaultMinVisibleBrightnessFraction = 0.0065;
-
 // Value for |level_to_percent_exponent_|, assuming that at least
 // |kMinLevelsForNonLinearScale| brightness levels are available -- if not, we
 // just use 1.0 to give us a linear scale.
@@ -137,6 +128,8 @@
 const int64_t InternalBacklightController::kMaxBrightnessSteps = 16;
 const double InternalBacklightController::kMinVisiblePercent =
     kMaxPercent / kMaxBrightnessSteps;
+const double InternalBacklightController::kDefaultMinVisibleBrightnessFraction =
+    0.0065;
 const int InternalBacklightController::kAmbientLightSensorTimeoutSec = 10;
 
 InternalBacklightController::InternalBacklightController()
@@ -186,14 +179,12 @@
   max_level_ = backlight_->GetMaxBrightnessLevel();
   current_level_ = backlight_->GetCurrentBrightnessLevel();
 
-  if (!prefs_->GetInt64(kMinVisibleBacklightLevelPref, &min_visible_level_))
-    min_visible_level_ = 1;
-  min_visible_level_ = std::max(
-      static_cast<int64_t>(
-          lround(kDefaultMinVisibleBrightnessFraction * max_level_)),
-      min_visible_level_);
-  CHECK_GT(min_visible_level_, 0);
-  min_visible_level_ = std::min(min_visible_level_, max_level_);
+  if (!prefs_->GetInt64(kMinVisibleBacklightLevelPref, &min_visible_level_)) {
+    min_visible_level_ = static_cast<int64_t>(
+        lround(kDefaultMinVisibleBrightnessFraction * max_level_));
+  }
+  min_visible_level_ = std::min(
+      std::max(min_visible_level_, static_cast<int64_t>(1)), max_level_);
 
   const double initial_percent = LevelToPercent(current_level_);
   ambient_light_brightness_percent_ = initial_percent;
diff --git a/power_manager/powerd/policy/internal_backlight_controller.h b/power_manager/powerd/policy/internal_backlight_controller.h
index e41446c..aff1e45 100644
--- a/power_manager/powerd/policy/internal_backlight_controller.h
+++ b/power_manager/powerd/policy/internal_backlight_controller.h
@@ -46,6 +46,16 @@
   // lowest brightness step before the screen is turned off.
   static const double kMinVisiblePercent;
 
+  // Minimum brightness, as a fraction of the maximum level in the range [0.0,
+  // 1.0], that is used as the bottom step before turning the backlight off
+  // entirely.  This is arbitrarily chosen but seems to be a reasonable
+  // marginally-visible brightness for a darkened room on current devices:
+  // http://crosbug.com/24569. A custom level can be set via the
+  // kMinVisibleBacklightLevelPref setting. This is a fraction of the
+  // driver-supplied maximum level rather than a percent so it won't change if
+  // kDefaultLevelToPercentExponent is modified.
+  static const double kDefaultMinVisibleBrightnessFraction;
+
   // If an ambient light reading hasn't been seen after this many seconds,
   // give up on waiting for the sensor to be initialized and just set
   // |use_ambient_light_| to false.
diff --git a/power_manager/powerd/policy/internal_backlight_controller_unittest.cc b/power_manager/powerd/policy/internal_backlight_controller_unittest.cc
index 894574d..3be558a 100644
--- a/power_manager/powerd/policy/internal_backlight_controller_unittest.cc
+++ b/power_manager/powerd/policy/internal_backlight_controller_unittest.cc
@@ -40,7 +40,7 @@
         initial_als_lux_(0),
         report_initial_als_reading_(true),
         report_initial_power_source_(true),
-        default_min_visible_level_(1),
+        default_min_visible_level_(-1),
         default_als_steps_("50.0 -1 400\n90.0 100 -1"),
         default_no_als_ac_brightness_("80.0"),
         default_no_als_battery_brightness_("60.0"),
@@ -52,7 +52,10 @@
   // event such that it should make its first adjustment to the backlight
   // brightness.
   virtual void Init(PowerSource power_source) {
-    prefs_.SetInt64(kMinVisibleBacklightLevelPref, default_min_visible_level_);
+    if (default_min_visible_level_ > 0) {
+      prefs_.SetInt64(kMinVisibleBacklightLevelPref,
+                      default_min_visible_level_);
+    }
     prefs_.SetString(kInternalBacklightAlsStepsPref, default_als_steps_);
     prefs_.SetString(kInternalBacklightNoAlsAcBrightnessPref,
                      default_no_als_ac_brightness_);
@@ -101,8 +104,8 @@
   bool report_initial_als_reading_;
   bool report_initial_power_source_;
 
-  // Default values for prefs.  Applied when Init() is called.
-  int64_t default_min_visible_level_;
+  // Default values for prefs. Applied when Init() is called.
+  int64_t default_min_visible_level_;  // Unset if non-positive.
   std::string default_als_steps_;
   std::string default_no_als_ac_brightness_;
   std::string default_no_als_battery_brightness_;
@@ -118,7 +121,7 @@
   default_min_visible_level_ = 100;
   default_als_steps_ = "50.0 -1 -1";
   Init(POWER_BATTERY);
-  EXPECT_EQ(default_min_visible_level_,
+  ASSERT_EQ(default_min_visible_level_,
             PercentToLevel(InternalBacklightController::kMinVisiblePercent));
   const int64_t kAlsLevel = PercentToLevel(50.0);
   EXPECT_EQ(kAlsLevel, backlight_.current_level());
@@ -866,5 +869,23 @@
             display_power_setter_.state());
 }
 
+TEST_F(InternalBacklightControllerTest, MinVisibleLevelPrefUndercutsDefault) {
+  // Set the min-visible-level pref below the computed default.
+  int64_t computed_min = static_cast<int64_t>(
+      lround(InternalBacklightController::kDefaultMinVisibleBrightnessFraction *
+             max_backlight_level_));
+  default_min_visible_level_ = static_cast<int64_t>(computed_min * 0.5);
+  ASSERT_GT(default_min_visible_level_, 0);
+  ASSERT_LT(default_min_visible_level_, computed_min);
+
+  // Set the brightness to 0%, increase it one step, and confirm that the level
+  // configured by the pref is used instead of the higher computed default.
+  Init(POWER_AC);
+  controller_->SetUserBrightnessPercent(
+      0.0, BacklightController::TRANSITION_INSTANT);
+  controller_->IncreaseUserBrightness();
+  EXPECT_EQ(default_min_visible_level_, backlight_.current_level());
+}
+
 }  // namespace policy
 }  // namespace power_manager