diff --git a/demo/demo.component.ts b/demo/demo.component.ts
index 54236d5..e965a62 100644
--- a/demo/demo.component.ts
+++ b/demo/demo.component.ts
@@ -1,4 +1,4 @@
-import { Component, ElementRef, ViewChild } from '@angular/core';
+import { Component, ElementRef, ViewChild, OnInit } from '@angular/core';
 import { FormBuilder, FormGroup } from '@angular/forms';
 import { CurrencyMaskInputMode } from '../src/currency-mask.config';
 
@@ -49,7 +49,7 @@ import { CurrencyMaskInputMode } from '../src/currency-mask.config';
     </form>
   `
 })
-export class DemoComponent {
+export class DemoComponent implements OnInit {
 
   @ViewChild('valueInput', { static: true }) valueInput: ElementRef;
 
@@ -58,7 +58,7 @@ export class DemoComponent {
     prefix: 'R$ ',
     thousands: '.',
     decimal: ',',
-    allowNegative: false,
+    allowNegative: true,
     nullable: true,
     max: 250_000_000,
     inputMode: CurrencyMaskInputMode.FINANCIAL,
@@ -69,7 +69,7 @@ export class DemoComponent {
 
   ngOnInit() {
     this.form = this.formBuilder.group({
-      value: null,
+      value: 0,
       inputMode: this.ngxCurrencyOptions.inputMode,
     });
 
@@ -77,7 +77,7 @@ export class DemoComponent {
       this.ngxCurrencyOptions.inputMode = val;
 
       // Clear and focus the value input when the input mode is changed.container
-      this.form.get('value').setValue(null);
+      this.form.get('value').setValue(0);
       this.valueInput.nativeElement.focus();
     });
 
diff --git a/src/input.service.ts b/src/input.service.ts
index 1ab138b..47d3f8e 100644
--- a/src/input.service.ts
+++ b/src/input.service.ts
@@ -138,8 +138,8 @@ export class InputService {
             }
         }
 
-        let isZero = newValue == 0;
-        let operator = (isNegative && allowNegative && !isZero) ? "-" : "";
+        // let isZero = newValue == 0;
+        let operator = (isNegative && allowNegative /*&& !isZero */) ? "-" : "";
         return operator + prefix + newRawValue + suffix;
     }
 
@@ -187,9 +187,9 @@ export class InputService {
     }
 
     changeToNegative(): void {
-        if (this.options.allowNegative && this.rawValue != "" && this.rawValue.charAt(0) != "-" && this.value != 0) {
+        if (this.options.allowNegative /*&& this.rawValue != ""*/ && this.rawValue.charAt(0) != "-" /*&& this.value != 0*/) {
             // Apply the mask to ensure the min and max values are enforced.
-            this.rawValue = this.applyMask(false, "-" + this.rawValue);
+            this.rawValue = this.applyMask(false, "-" + (this.rawValue ? this.rawValue : '0'));
         }
     }
 
@@ -213,7 +213,7 @@ export class InputService {
         selectionEnd = Math.min(suffixStart, Math.max(selectionEnd, prefix.length));
         selectionStart = Math.min(suffixStart, Math.max(selectionStart, prefix.length));
 
-        // Check if selection was entirely in the prefix or suffix. 
+        // Check if selection was entirely in the prefix or suffix.
         if (selectionStart === selectionEnd &&
             this.inputSelection.selectionStart !== this.inputSelection.selectionEnd) {
             this.updateFieldValue(selectionStart);
@@ -226,7 +226,7 @@ export class InputService {
         }
 
         let shiftSelection = 0;
-        let insertChars = '';   
+        let insertChars = '';
         if (selectionEnd === selectionStart) {
             if (keyCode == 8) {
                 if (selectionStart <= prefix.length) {