diff --git a/README.md b/README.md
index e8b7aedd9..4028e7761 100644
--- a/README.md
+++ b/README.md
@@ -167,7 +167,7 @@ Validator                               | Description
 **isStrongPassword(str [, options])**   | check if the string can be considered a strong password or not. Allows for custom requirements or scoring rules. If `returnScore` is true, then the function returns an integer score for the password rather than a boolean.<br/>Default options: <br/>`{ minLength: 8, minLowercase: 1, minUppercase: 1, minNumbers: 1, minSymbols: 1, returnScore: false, pointsPerUnique: 1, pointsPerRepeat: 0.5, pointsForContainingLower: 10, pointsForContainingUpper: 10, pointsForContainingNumber: 10, pointsForContainingSymbol: 10 }`
 **isTime(str [, options])**             | check if the string is a valid time e.g. [`23:01:59`, new Date().toLocaleTimeString()].<br/><br/> `options` is an object which can contain the keys `hourFormat` or `mode`.<br/><br/>`hourFormat` is a key and defaults to `'hour24'`.<br/><br/>`mode` is a key and defaults to `'default'`. <br/><br/>`hourFormat` can contain the values `'hour12'` or `'hour24'`, `'hour24'` will validate hours in 24 format and `'hour12'` will validate hours in 12 format. <br/><br/>`mode` can contain the values `'default', 'withSeconds', withOptionalSeconds`, `'default'` will validate `HH:MM` format, `'withSeconds'` will validate the `HH:MM:SS` format, `'withOptionalSeconds'` will validate `'HH:MM'` and `'HH:MM:SS'` formats.
 **isTaxID(str, locale)**                | check if the string is a valid Tax Identification Number. Default locale is `en-US`.<br/><br/>More info about exact TIN support can be found in `src/lib/isTaxID.js`.<br/><br/>Supported locales: `[ 'bg-BG', 'cs-CZ', 'de-AT', 'de-DE', 'dk-DK', 'el-CY', 'el-GR', 'en-CA', 'en-GB', 'en-IE', 'en-IN', 'en-US', 'es-AR', 'es-ES', 'et-EE', 'fi-FI', 'fr-BE', 'fr-CA', 'fr-FR', 'fr-LU', 'hr-HR', 'hu-HU', 'it-IT', 'lb-LU', 'lt-LT', 'lv-LV', 'mt-MT', 'nl-BE', 'nl-NL', 'pl-PL', 'pt-BR', 'pt-PT', 'ro-RO', 'sk-SK', 'sl-SI', 'sv-SE', 'uk-UA']`.
-**isURL(str [, options])**              | check if the string is a URL.<br/><br/>`options` is an object which defaults to `{ protocols: ['http','https','ftp'], require_tld: true, require_protocol: false, require_host: true, require_port: false, require_valid_protocol: true, allow_underscores: false, host_whitelist: false, host_blacklist: false, allow_trailing_dot: false, allow_protocol_relative_urls: false, allow_fragments: true, allow_query_components: true, disallow_auth: false, validate_length: true }`.<br/><br/>`protocols` - valid protocols can be modified with this option.<br/>`require_tld` - If set to false isURL will not check if the URL's host includes a top-level domain.<br/>`require_protocol` - **RECOMMENDED** if set to true isURL will return false if protocol is not present in the URL. Without this setting, some malicious URLs cannot be distinguishable from a valid URL with authentication information.<br/>`require_host` - if set to false isURL will not check if host is present in the URL.<br/>`require_port` - if set to true isURL will check if port is present in the URL.<br/>`require_valid_protocol` - isURL will check if the URL's protocol is present in the protocols option.<br/>`allow_underscores` - if set to true, the validator will allow underscores in the URL.<br/>`host_whitelist` - if set to an array of strings or regexp, and the domain matches none of the strings defined in it, the validation fails.<br/>`host_blacklist` - if set to an array of strings or regexp, and the domain matches any of the strings defined in it, the validation fails.<br/>`allow_trailing_dot` - if set to true, the validator will allow the domain to end with a `.` character.<br/>`allow_protocol_relative_urls` - if set to true protocol relative URLs will be allowed.<br/>`allow_fragments` - if set to false isURL will return false if fragments are present.<br/>`allow_query_components` - if set to false isURL will return false if query components are present.<br/>`disallow_auth` - if set to true, the validator will fail if the URL contains an authentication component, e.g. `http://username:password@example.com`.<br/>`validate_length` - if set to false isURL will skip string length validation. `max_allowed_length` will be ignored if this is set as `false`.<br/>`max_allowed_length` - if set, isURL will not allow URLs longer than the specified value (default is 2084 that IE maximum URL length).<br/>
+**isURL(str [, options])**              | check if the string is a URL.<br/><br/>`options` is an object which defaults to `{ protocols: ['http','https','ftp'], require_tld: true, require_protocol: false, require_protocol_slashes: false, require_host: true, require_port: false, require_valid_protocol: true, allow_underscores: false, host_whitelist: false, host_blacklist: false, allow_trailing_dot: false, allow_protocol_relative_urls: false, allow_fragments: true, allow_query_components: true, disallow_auth: false, validate_length: true }`.<br/><br/>`protocols` - valid protocols can be modified with this option.<br/>`require_tld` - If set to false isURL will not check if the URL's host includes a top-level domain.<br/>`require_protocol` - **RECOMMENDED** if set to true isURL will return false if protocol is not present in the URL. Without this setting, some malicious URLs cannot be distinguishable from a valid URL with authentication information.<br/>`require_protocol_slashes` - if set to true, an explicit protocol must be followed by `//` (for example, `https://example.com` passes and `https:example.com` fails). This does not require a protocol; use `require_protocol: true` for that.<br/>`require_host` - if set to false isURL will not check if host is present in the URL.<br/>`require_port` - if set to true isURL will check if port is present in the URL.<br/>`require_valid_protocol` - isURL will check if the URL's protocol is present in the protocols option.<br/>`allow_underscores` - if set to true, the validator will allow underscores in the URL.<br/>`host_whitelist` - if set to an array of strings or regexp, and the domain matches none of the strings defined in it, the validation fails.<br/>`host_blacklist` - if set to an array of strings or regexp, and the domain matches any of the strings defined in it, the validation fails.<br/>`allow_trailing_dot` - if set to true, the validator will allow the domain to end with a `.` character.<br/>`allow_protocol_relative_urls` - if set to true protocol relative URLs will be allowed.<br/>`allow_fragments` - if set to false isURL will return false if fragments are present.<br/>`allow_query_components` - if set to false isURL will return false if query components are present.<br/>`disallow_auth` - if set to true, the validator will fail if the URL contains an authentication component, e.g. `http://username:password@example.com`.<br/>`validate_length` - if set to false isURL will skip string length validation. `max_allowed_length` will be ignored if this is set as `false`.<br/>`max_allowed_length` - if set, isURL will not allow URLs longer than the specified value (default is 2084 that IE maximum URL length).<br/>
 **isULID(str)**                         | check if the string is a [ULID](https://github.com/ulid/spec).
 **isUUID(str [, version])**             | check if the string is an RFC9562 UUID.<br/>`version` is one of `'1'`-`'8'`, `'nil'`, `'max'`, `'all'` or `'loose'`. The `'loose'` option checks if the string is a UUID-like string with hexadecimal values, ignoring RFC9565.
 **isVariableWidth(str)**                | check if the string contains a mixture of full and half-width chars.
diff --git a/src/lib/isURL.js b/src/lib/isURL.js
index 600a91dec..cd97412e4 100644
--- a/src/lib/isURL.js
+++ b/src/lib/isURL.js
@@ -12,6 +12,7 @@ options for isURL method
 protocols - valid protocols can be modified with this option.
 require_tld - If set to false isURL will not check if the URL's host includes a top-level domain.
 require_protocol - if set to true isURL will return false if protocol is not present in the URL.
+require_protocol_slashes - if set to true, an explicit protocol must be followed by `//`.
 require_host - if set to false isURL will not check if host is present in the URL.
 require_port - if set to true isURL will check if port is present in the URL.
 require_valid_protocol - isURL will check if the URL's protocol is present in the protocols option.
@@ -39,6 +40,7 @@ const default_url_options = {
   protocols: ['http', 'https', 'ftp'],
   require_tld: true,
   require_protocol: false,
+  require_protocol_slashes: false,
   require_host: true,
   require_port: false,
   require_valid_protocol: true,
@@ -91,6 +93,11 @@ export default function isURL(url, options) {
   let had_explicit_protocol = false;
 
   const cleanUpProtocol = (potential_protocol) => {
+    const after_protocol = url.substring(protocol_match[0].length);
+    if (options.require_protocol_slashes && after_protocol.slice(0, 2) !== '//') {
+      return false;
+    }
+
     had_explicit_protocol = true;
     protocol = potential_protocol.toLowerCase();
 
@@ -100,7 +107,7 @@ export default function isURL(url, options) {
     }
 
     // Remove the protocol from the URL string.
-    return url.substring(protocol_match[0].length);
+    return after_protocol;
   };
 
   if (protocol_match) {
diff --git a/test/validators.test.js b/test/validators.test.js
index 98d2a12ff..3027be1e3 100644
--- a/test/validators.test.js
+++ b/test/validators.test.js
@@ -563,6 +563,79 @@ describe('Validators', () => {
     });
   });
 
+  it('should require slashes after an explicit protocol when requested', () => {
+    test({
+      validator: 'isURL',
+      args: [{ require_protocol_slashes: true }],
+      valid: [
+        'http://example.com',
+        'HTTPS://example.com/path?query=value#fragment',
+        'ftp://example.com',
+        'https://user:password@example.com',
+        'https://[::1]:8080/path',
+        'example.com:8080/path',
+        'user:password@example.com',
+      ],
+      invalid: [
+        'http:example.com',
+        'https:example.com',
+        'HTTPS:example.com/path?query=value#fragment',
+        'ftp:example.com',
+        'https:/example.com',
+        '//example.com',
+      ],
+    });
+  });
+
+  it('should combine protocol slashes with requiring a protocol', () => {
+    test({
+      validator: 'isURL',
+      args: [{ require_protocol_slashes: true, require_protocol: true }],
+      valid: ['https://example.com'],
+      invalid: ['https:example.com', 'example.com', 'user:password@example.com'],
+    });
+  });
+
+  it('should allow protocol-relative URLs when only protocol slashes are required', () => {
+    test({
+      validator: 'isURL',
+      args: [{ require_protocol_slashes: true, allow_protocol_relative_urls: true }],
+      valid: ['//example.com', 'example.com', 'https://example.com'],
+      invalid: ['https:example.com'],
+    });
+  });
+
+  it('should require slashes for custom protocols when requested', () => {
+    test({
+      validator: 'isURL',
+      args: [{ require_protocol_slashes: true, protocols: ['custom'] }],
+      valid: ['custom://example.com'],
+      invalid: ['custom:example.com'],
+    });
+    test({
+      validator: 'isURL',
+      args: [{ require_protocol_slashes: true, require_valid_protocol: false }],
+      valid: ['custom://example.com'],
+      invalid: ['custom:example.com'],
+    });
+  });
+
+  it('should keep accepting protocols without slashes by default', () => {
+    const optionsList = [
+      undefined,
+      { require_protocol_slashes: false },
+      { require_protocol: true },
+    ];
+    optionsList.forEach((options) => {
+      test({
+        validator: 'isURL',
+        args: [options],
+        valid: ['http:example.com', 'https:example.com', 'ftp:example.com'],
+        invalid: [],
+      });
+    });
+  });
+
   it('should validate file URLs without a host', () => {
     test({
       validator: 'isURL',