diff --git a/public/app/features/alerting/unified/components/mute-timings/MuteTimingTimeInterval.test.tsx b/public/app/features/alerting/unified/components/mute-timings/MuteTimingTimeInterval.test.tsx
new file mode 100644
index 00000000000..ef440225088
--- /dev/null
+++ b/public/app/features/alerting/unified/components/mute-timings/MuteTimingTimeInterval.test.tsx
@@ -0,0 +1,53 @@
+import { validateDaysOfMonth } from './MuteTimingTimeInterval';
+
+describe('validateDaysOfMonth', () => {
+  it('should return true for valid empty value', () => {
+    expect(validateDaysOfMonth('')).toBe(true);
+    expect(validateDaysOfMonth(undefined)).toBe(true);
+  });
+
+  it('should return true for valid single days', () => {
+    expect(validateDaysOfMonth('1')).toBe(true);
+    expect(validateDaysOfMonth('15')).toBe(true);
+    expect(validateDaysOfMonth('31')).toBe(true);
+    expect(validateDaysOfMonth('-1')).toBe(true);
+    expect(validateDaysOfMonth('-30')).toBe(true);
+  });
+
+  it('should return true for valid day ranges', () => {
+    expect(validateDaysOfMonth('1:5')).toBe(true);
+    expect(validateDaysOfMonth('1:5, 10:15')).toBe(true);
+    expect(validateDaysOfMonth('1:5, 10, 15, 20:25')).toBe(true);
+    expect(validateDaysOfMonth('1:5,10:15')).toBe(true);
+    expect(validateDaysOfMonth('1:5,10,15,20:25')).toBe(true);
+    expect(validateDaysOfMonth('-30:-1')).toBe(true);
+  });
+
+  it('should return true for valid mixed positive and negative days', () => {
+    expect(validateDaysOfMonth('1, -1')).toBe(true);
+    expect(validateDaysOfMonth('1:5, -10, -15')).toBe(true);
+    expect(validateDaysOfMonth('1,-1')).toBe(true);
+    expect(validateDaysOfMonth('1:5,-10,-15')).toBe(true);
+  });
+
+  it('should return error message for invalid format with non-numeric characters', () => {
+    expect(validateDaysOfMonth('1a')).toBe('Invalid day');
+    expect(validateDaysOfMonth('a')).toBe('Invalid day');
+    expect(validateDaysOfMonth('1-5')).toBe('Invalid day');
+    expect(validateDaysOfMonth('1 5')).toBe('Invalid day');
+    expect(validateDaysOfMonth('1..5')).toBe('Invalid day');
+  });
+
+  it('should return error message for out of range days', () => {
+    expect(validateDaysOfMonth('0')).toBe('Invalid day');
+    expect(validateDaysOfMonth('32')).toBe('Invalid day');
+    expect(validateDaysOfMonth('-32')).toBe('Invalid day');
+    expect(validateDaysOfMonth('-0')).toBe('Invalid day');
+  });
+
+  it('should return error message for mixed valid and invalid days', () => {
+    expect(validateDaysOfMonth('1, 32')).toBe('Invalid day');
+    expect(validateDaysOfMonth('1:5, 15a')).toBe('Invalid day');
+    expect(validateDaysOfMonth('1, abc')).toBe('Invalid day');
+  });
+});
diff --git a/public/app/features/alerting/unified/components/mute-timings/MuteTimingTimeInterval.tsx b/public/app/features/alerting/unified/components/mute-timings/MuteTimingTimeInterval.tsx
index d25c002fe0d..49307778402 100644
--- a/public/app/features/alerting/unified/components/mute-timings/MuteTimingTimeInterval.tsx
+++ b/public/app/features/alerting/unified/components/mute-timings/MuteTimingTimeInterval.tsx
@@ -72,21 +72,13 @@ export const MuteTimingTimeInterval = () => {
                 </Field>
                 <Field
                   label="Days of the month"
-                  description="The days of the month, 1-31, of a month. Negative values can be used to represent days which begin at the end of the month"
+                  description="The days of the month, 1:31, of a month. Negative values can be used to represent days which begin at the end of the month"
                   invalid={!!errors.time_intervals?.[timeIntervalIndex]?.days_of_month}
                   error={errors.time_intervals?.[timeIntervalIndex]?.days_of_month?.message}
                 >
                   <Input
                     {...register(`time_intervals.${timeIntervalIndex}.days_of_month`, {
-                      validate: (value) =>
-                        validateArrayField(
-                          value,
-                          (day) => {
-                            const parsedDay = parseInt(day, 10);
-                            return (parsedDay > -31 && parsedDay < 0) || (parsedDay > 0 && parsedDay < 32);
-                          },
-                          'Invalid day'
-                        ),
+                      validate: validateDaysOfMonth,
                     })}
                     width={50}
                     // @ts-ignore react-hook-form doesn't handle nested field arrays well
@@ -195,6 +187,22 @@ const parseDays = (input: string): string[] => {
   return uniq(parsedDays);
 };
 
+export function validateDaysOfMonth(value: string | undefined) {
+  return validateArrayField(
+    value,
+    (day) => {
+      // Ensure the value contains ONLY digits with an optional negative sign
+      // This rejects any non-numeric characters or mixed inputs like "3-10"
+      if (!/^-?\d+$/.test(day)) {
+        return false;
+      }
+      const parsedDay = parseInt(day, 10);
+      return (parsedDay > -31 && parsedDay < 0) || (parsedDay > 0 && parsedDay < 32);
+    },
+    'Invalid day'
+  );
+}
+
 // parse monday:wednesday to ["monday", "tuesday", "wednesday"]
 function parseWeekdayRange(input: string): string[] {
   const [start = '', end = ''] = input.split(':');