diff --git a/qt-ui/diveplanner.ui b/qt-ui/diveplanner.ui
index 55208abb3..558be069d 100644
--- a/qt-ui/diveplanner.ui
+++ b/qt-ui/diveplanner.ui
@@ -101,25 +101,22 @@
        </item>
        <item row="5" column="0">
         <widget class="QSpinBox" name="gflow">
-         <property name="suffix">
-          <string>%</string>
-         </property>
          <property name="minimum">
           <number>1</number>
          </property>
          <property name="maximum">
-          <number>100</number>
+          <number>150</number>
          </property>
         </widget>
        </item>
        <item row="5" column="1">
         <widget class="QSpinBox" name="gfhigh">
-         <property name="suffix">
-          <string>%</string>
-         </property>
          <property name="minimum">
           <number>1</number>
          </property>
+         <property name="maximum">
+          <number>150</number>
+         </property>
         </widget>
        </item>
        <item row="6" column="0">
diff --git a/qt-ui/preferences.cpp b/qt-ui/preferences.cpp
index 5a1a2a5e2..f8b24da42 100644
--- a/qt-ui/preferences.cpp
+++ b/qt-ui/preferences.cpp
@@ -15,10 +15,28 @@ PreferencesDialog::PreferencesDialog(QWidget* parent, Qt::WindowFlags f) : QDial
 {
 	ui.setupUi(this);
 	connect(ui.buttonBox, SIGNAL(clicked(QAbstractButton*)), this, SLOT(buttonClicked(QAbstractButton*)));
+	connect(ui.gflow, SIGNAL(valueChanged(int)), this, SLOT(gflowChanged(int)));
+	connect(ui.gfhigh, SIGNAL(valueChanged(int)), this, SLOT(gfhighChanged(int)));
 	setUiFromPrefs();
 	rememberPrefs();
 }
 
+void PreferencesDialog::gflowChanged(int gf)
+{
+	if (gf > 100)
+		ui.gflow->setStyleSheet("* { color: red; }");
+	else
+		ui.gflow->setStyleSheet("");
+}
+
+void PreferencesDialog::gfhighChanged(int gf)
+{
+	if (gf > 100)
+		ui.gfhigh->setStyleSheet("* { color: red; }");
+	else
+		ui.gfhigh->setStyleSheet("");
+}
+
 void PreferencesDialog::showEvent(QShowEvent *event)
 {
 	setUiFromPrefs();
diff --git a/qt-ui/preferences.h b/qt-ui/preferences.h
index fb0fcbc94..dbc17cb9f 100644
--- a/qt-ui/preferences.h
+++ b/qt-ui/preferences.h
@@ -22,6 +22,9 @@ public slots:
 	void syncSettings();
 	void restorePrefs();
 	void rememberPrefs();
+	void gflowChanged(int gf);
+	void gfhighChanged(int gf);
+
 
 private:
 	explicit PreferencesDialog(QWidget* parent = 0, Qt::WindowFlags f = 0);
diff --git a/qt-ui/preferences.ui b/qt-ui/preferences.ui
index e80cc8493..7b6f3e596 100644
--- a/qt-ui/preferences.ui
+++ b/qt-ui/preferences.ui
@@ -779,7 +779,14 @@
              </widget>
             </item>
             <item row="0" column="1">
-             <widget class="QSpinBox" name="gflow"/>
+             <widget class="QSpinBox" name="gflow">
+              <property name="minimum">
+               <number>1</number>
+              </property>
+              <property name="maximum">
+               <number>150</number>
+              </property>
+             </widget>
             </item>
             <item row="1" column="0">
              <widget class="QLabel" name="label_20">
@@ -789,7 +796,14 @@
              </widget>
             </item>
             <item row="1" column="1">
-             <widget class="QSpinBox" name="gfhigh"/>
+             <widget class="QSpinBox" name="gfhigh">
+              <property name="minimum">
+               <number>1</number>
+              </property>
+              <property name="maximum">
+               <number>150</number>
+              </property>
+             </widget>
             </item>
             <item row="2" column="0" colspan="2">
              <widget class="QCheckBox" name="gf_low_at_maxdepth">