diff --git a/addons/portal/static/src/js/portal_name_and_signature.js b/addons/portal/static/src/js/portal_name_and_signature.js
index 20ce8d5ae22..18e5a6ee2a8 100644
--- a/addons/portal/static/src/js/portal_name_and_signature.js
+++ b/addons/portal/static/src/js/portal_name_and_signature.js
@@ -19,6 +19,7 @@ var NameAndSignature = Widget.extend({
         'input .o_portal_sign_name_input': '_onInputSignName',
         // signature
         'click .o_portal_sign_signature': '_onClickSignature',
+        'change .o_portal_sign_signature': '_onChangeSignature',
         // draw
         'click .o_portal_sign_draw_button': '_onClickSignDrawButton',
         'click .o_portal_sign_draw_clear a': '_onClickSignDrawClear',
@@ -180,7 +181,7 @@ var NameAndSignature = Widget.extend({
      */
     isSignatureEmpty: function () {
         var signature = this.$signatureField.jSignature('getData');
-        return signature ? this.emptySignature === signature : true;
+        return signature && this.emptySignature ? this.emptySignature === signature : true;
     },
     /**
      * (Re)initializes the signature area:
@@ -390,6 +391,7 @@ var NameAndSignature = Widget.extend({
                     height
                 );
                 _.extend(context, ignoredContext);
+                self.trigger_up('signature_changed');
             }, 0);
         };
         image.src = imgSrc;
@@ -432,6 +434,29 @@ var NameAndSignature = Widget.extend({
             }
         }, 0);
     },
+    /**
+     * Waits for the signature to be not empty and triggers up the event
+     * `signature_changed`.
+     * This is necessary because some methods of jSignature are async but
+     * they don't return a promise and don't trigger any event.
+     *
+     * @private
+     * @param {Deferred} [def=Deferred] - Deferred that will be returned by
+     *  the method and resolved when the signature is not empty anymore.
+     * @returns {Deferred}
+     */
+    _waitForSignatureNotEmpty: function (def) {
+        def = def || $.Deferred();
+        if (!this.isSignatureEmpty()) {
+            this.trigger_up('signature_changed');
+            def.resolve();
+        } else {
+            // Use the existing def to prevent the method from creating a new
+            // one at every loop.
+            setTimeout(this._waitForSignatureNotEmpty.bind(this, def), 10);
+        }
+        return def;
+    },
 
     //----------------------------------------------------------------------
     // Handlers
@@ -521,6 +546,15 @@ var NameAndSignature = Widget.extend({
         this.$loadFile.find('input').click();
         this.setMode('load');
     },
+    /**
+     * Triggers up the signature change event.
+     *
+     * @private
+     * @param {Event} ev
+     */
+    _onChangeSignature: function (ev) {
+        this.trigger_up('signature_changed');
+    },
     /**
      * Handles change on load file input: displays the loaded image if the
      * format is correct, or diplays an error otherwise.
diff --git a/addons/portal/static/src/js/portal_signature.js b/addons/portal/static/src/js/portal_signature.js
index f2741c7d741..f9a83caa224 100644
--- a/addons/portal/static/src/js/portal_signature.js
+++ b/addons/portal/static/src/js/portal_signature.js
@@ -20,6 +20,9 @@ odoo.define('portal.signature_form', function (require) {
         events: {
             'click .o_portal_sign_submit': '_onClickSignSubmit',
         },
+        custom_events: {
+            'signature_changed': '_onChangeSignature',
+        },
 
         /**
          * Overridden to allow options.
@@ -134,6 +137,15 @@ odoo.define('portal.signature_form', function (require) {
                 }
             });
         },
+        /**
+         * Toggles the submit button depending on the signature state.
+         *
+         * @private
+         */
+        _onChangeSignature: function () {
+            var isEmpty = this.nameAndSignature.isSignatureEmpty();
+            this.$confirm_btn.prop('disabled', isEmpty);
+        },
     });
 
     return {
diff --git a/addons/portal/static/src/xml/portal_signature.xml b/addons/portal/static/src/xml/portal_signature.xml
index 9904ce88407..57fd067b4a9 100644
--- a/addons/portal/static/src/xml/portal_signature.xml
+++ b/addons/portal/static/src/xml/portal_signature.xml
@@ -7,7 +7,7 @@
             <div class="o_portal_sign_name_and_signature"/>
             <div class="o_portal_sign_controls my-3">
                 <div class="text-center my-3">
-                    <button type="submit" class="o_portal_sign_submit btn btn-primary">
+                    <button type="submit" class="o_portal_sign_submit btn btn-primary" disabled="disabled">
                         <i class="fa fa-check"/>
                         <t t-esc="widget.sendLabel"/>
                     </button>
diff --git a/addons/sale/static/src/js/sale_tour_sale_signature.js b/addons/sale/static/src/js/sale_tour_sale_signature.js
index ffbdd849ffb..f45bf2d22e7 100644
--- a/addons/sale/static/src/js/sale_tour_sale_signature.js
+++ b/addons/sale/static/src/js/sale_tour_sale_signature.js
@@ -19,10 +19,20 @@ tour.register('sale_signature', {
         content: "click sign",
         trigger: 'a:contains("Sign")',
     },
+    {
+        content: "check submit is disabled",
+        trigger: '.o_portal_sign_submit:disabled',
+        run: function () {},
+    },
     {
         content: "click Auto",
         trigger: '.o_portal_sign_auto_button',
     },
+    {
+        content: "check submit is enabled",
+        trigger: '.o_portal_sign_submit:enabled',
+        run: function () {},
+    },
     {
         content: "click select style",
         trigger: '.o_portal_sign_auto_select_style a',
@@ -33,7 +43,7 @@ tour.register('sale_signature', {
     },
     {
         content: "click submit",
-        trigger: '.o_portal_sign_submit',
+        trigger: '.o_portal_sign_submit:enabled',
     },
     {
         content: "check it's confirmed",