diff --git a/app/src/main/java/com/eveningoutpost/dexdrip/utils/Preferences.java b/app/src/main/java/com/eveningoutpost/dexdrip/utils/Preferences.java
index 4d43f46ad0..07785d3d8b 100644
--- a/app/src/main/java/com/eveningoutpost/dexdrip/utils/Preferences.java
+++ b/app/src/main/java/com/eveningoutpost/dexdrip/utils/Preferences.java
@@ -1,5 +1,7 @@
 package com.eveningoutpost.dexdrip.utils;
 
+import static com.eveningoutpost.dexdrip.EditAlertActivity.unitsConvert2Disp;
+import static com.eveningoutpost.dexdrip.models.JoH.tolerantParseDouble;
 import static com.eveningoutpost.dexdrip.utils.DexCollectionType.getBestCollectorHardwareName;
 import static com.eveningoutpost.dexdrip.xdrip.gs;
 
@@ -192,6 +194,8 @@ public class Preferences extends BasePreferenceActivity implements SearchPrefere
     private void refreshFragments() {
         refreshFragments(null);
     }
+    public static final double MIN_GLUCOSE_INPUT = 40; // The smallest acceptable input glucose value in mg/dL
+    public static final double MAX_GLUCOSE_INPUT = 400; // The largest acceptable input glucose value in mg/dL
 
     private void refreshFragments(final String jumpTo) {
         this.preferenceFragment = new AllPrefsFragment(jumpTo);
@@ -749,16 +753,21 @@ public boolean onPreferenceChange(Preference preference, Object value) {
         }
     };
 
-    private static Preference.OnPreferenceChangeListener sBindNumericUnitizedPreferenceSummaryToValueListener = new Preference.OnPreferenceChangeListener() { // This listener adds glucose unit in addition to the value to the summary
+    private static Preference.OnPreferenceChangeListener sBindNumericUnitizedPreferenceSummaryToValueListener = new Preference.OnPreferenceChangeListener() { // This listener adds glucose unit in addition to the value to the summary and rejects out-of-range inputs
         @Override
         public boolean onPreferenceChange(Preference preference, Object value) {
             String stringValue = value.toString();
             if (isNumeric(stringValue)) {
                 final boolean domgdl = Pref.getString("units", "mgdl").equals("mgdl"); // Identify which unit is chosen
+                double submissionMgdl = domgdl ? tolerantParseDouble(stringValue) : tolerantParseDouble(stringValue) * Constants.MMOLL_TO_MGDL;
+                if (submissionMgdl > MAX_GLUCOSE_INPUT || submissionMgdl < MIN_GLUCOSE_INPUT) {
+                    JoH.static_toast_long(xdrip.gs(R.string.the_value_must_be_between_min_and_max, unitsConvert2Disp(domgdl, MIN_GLUCOSE_INPUT), unitsConvert2Disp(domgdl, MAX_GLUCOSE_INPUT)));
+                    return false; // Reject input if out of range
+                }
                 preference.setSummary(stringValue + "  " + (domgdl ? "mg/dl" : "mmol/l")); // Set the summary to show the value followed by the chosen unit
-                return true;
+                return true; // Accept input as it is numeric and in range
             }
-            return false;
+            return false; // Reject input if not numeric
         }
     };
     private static Preference.OnPreferenceChangeListener sBindPreferenceTitleAppendToValueListenerUpdateChannel = new Preference.OnPreferenceChangeListener() {
@@ -1009,7 +1018,7 @@ private static void bindPreferenceSummaryToValueAndEnsureNumeric(Preference pref
                         .getString(preference.getKey(), ""));
     }
 
-    private static void bindPreferenceSummaryToUnitizedValueAndEnsureNumeric(Preference preference) { // Use this to show the value as well as the corresponding glucose unit as the summary
+    private static void bindPreferenceSummaryToUnitizedValueAndEnsureNumeric(Preference preference) { // Use this to show the value as well as the corresponding glucose unit as the summary, and reject out-of-range inputs
         preference.setOnPreferenceChangeListener(sBindNumericUnitizedPreferenceSummaryToValueListener);
         sBindNumericUnitizedPreferenceSummaryToValueListener.onPreferenceChange(preference,
                 PreferenceManager
diff --git a/app/src/main/res/values/strings.xml b/app/src/main/res/values/strings.xml
index 3a5c7c3b72..96a00945f8 100644
--- a/app/src/main/res/values/strings.xml
+++ b/app/src/main/res/values/strings.xml
@@ -243,6 +243,7 @@
     <string name="persistent_high_alert">Persistent High Alert</string>
     <string name="persistent_high_alert_enable">Enable</string>
     <string name="title_persistent_high_threshold">Threshold</string>
+    <string name="the_value_must_be_between_min_and_max">The value must be between %1$s and %2$s</string>
     <string name="forecasted_low_alert">Forecasted Low Alert</string>
     <string name="extrapolate_data_to_try_to_predict_lows">Extrapolate data to try to predict lows</string>
     <string name="alarm_at_forecasted_low_mins">Alarm at Forecasted Low mins</string>