diff --git a/index.js b/index.js
index dc03609..e946489 100644
--- a/index.js
+++ b/index.js
@@ -47,8 +47,16 @@
         query = splitted[4];
         fragment = splitted[5];
 
-        // scheme and path are required, though the path can be empty
-        if (!(scheme && scheme.length && path.length >= 0)) return;
+        if (!scheme && /^\/\//.test(value)) {
+            scheme = "";
+        } else {
+
+            // scheme and path are required, though the path can be empty
+            if (!(scheme && scheme.length && path.length >= 0)) return;
+    
+            // scheme must begin with a letter, then consist of letters, digits, +, ., or -
+            if (!/^[a-z][a-z0-9\+\-\.]*$/.test(scheme.toLowerCase()))  return;
+        }
 
         // if authority is present, the path must be empty or begin with a /
         if (authority && authority.length) {
@@ -58,9 +66,6 @@
             if (/^\/\//.test(path)) return;
         }
 
-        // scheme must begin with a letter, then consist of letters, digits, +, ., or -
-        if (!/^[a-z][a-z0-9\+\-\.]*$/.test(scheme.toLowerCase()))  return;
-
         // re-assemble the URL per section 5.3 in RFC 3986
         out += scheme + ':';
         if (authority && authority.length) {
diff --git a/package-lock.json b/package-lock.json
new file mode 100644
index 0000000..cf36424
--- /dev/null
+++ b/package-lock.json
@@ -0,0 +1,430 @@
+{
+  "name": "valid-url",
+  "version": "1.0.5",
+  "lockfileVersion": 1,
+  "requires": true,
+  "dependencies": {
+    "abbrev": {
+      "version": "1.1.1",
+      "resolved": "https://registry.npmjs.org/abbrev/-/abbrev-1.1.1.tgz",
+      "integrity": "sha512-nne9/IiQ/hzIhY6pdDnbBtz7DjPTKrY00P/zvPSm5pOFkl6xuGrGnXn/VtTNNfNtAfZ9/1RtehkszU9qcTii0Q==",
+      "dev": true
+    },
+    "balanced-match": {
+      "version": "1.0.0",
+      "resolved": "https://registry.npmjs.org/balanced-match/-/balanced-match-1.0.0.tgz",
+      "integrity": "sha1-ibTRmasr7kneFk6gK4nORi1xt2c=",
+      "dev": true
+    },
+    "brace-expansion": {
+      "version": "1.1.11",
+      "resolved": "https://registry.npmjs.org/brace-expansion/-/brace-expansion-1.1.11.tgz",
+      "integrity": "sha512-iCuPHDFgrHX7H2vEI/5xpz07zSHB00TpugqhmYtVmMO6518mCuRMoOYFldEBl0g187ufozdaHgWKcYFb61qGiA==",
+      "dev": true,
+      "requires": {
+        "balanced-match": "^1.0.0",
+        "concat-map": "0.0.1"
+      }
+    },
+    "buffer-equal": {
+      "version": "0.0.2",
+      "resolved": "https://registry.npmjs.org/buffer-equal/-/buffer-equal-0.0.2.tgz",
+      "integrity": "sha1-7Lt5D1aNQAmKYkK1SAXHWAXrk48=",
+      "dev": true
+    },
+    "bunker": {
+      "version": "0.1.2",
+      "resolved": "https://registry.npmjs.org/bunker/-/bunker-0.1.2.tgz",
+      "integrity": "sha1-yImSRkqOKm7ehpMDdfkrWAd++Xw=",
+      "dev": true,
+      "requires": {
+        "burrito": ">=0.2.5 <0.3"
+      }
+    },
+    "burrito": {
+      "version": "0.2.12",
+      "resolved": "https://registry.npmjs.org/burrito/-/burrito-0.2.12.tgz",
+      "integrity": "sha1-0NbmrIHV6ZeJxvpKzLCwAx6lT2s=",
+      "dev": true,
+      "requires": {
+        "traverse": "~0.5.1",
+        "uglify-js": "~1.1.1"
+      },
+      "dependencies": {
+        "traverse": {
+          "version": "0.5.2",
+          "resolved": "https://registry.npmjs.org/traverse/-/traverse-0.5.2.tgz",
+          "integrity": "sha1-4gPFjV9/DjfbbnTArLkpuwm2HYU=",
+          "dev": true
+        }
+      }
+    },
+    "charm": {
+      "version": "0.1.2",
+      "resolved": "https://registry.npmjs.org/charm/-/charm-0.1.2.tgz",
+      "integrity": "sha1-BsIe7RobBq62dVPNxT4jJ0usIpY=",
+      "dev": true
+    },
+    "cli": {
+      "version": "1.0.1",
+      "resolved": "https://registry.npmjs.org/cli/-/cli-1.0.1.tgz",
+      "integrity": "sha1-IoF1NPJL+klQw01TLUjsvGIbjBQ=",
+      "dev": true,
+      "requires": {
+        "exit": "0.1.2",
+        "glob": "^7.1.1"
+      }
+    },
+    "concat-map": {
+      "version": "0.0.1",
+      "resolved": "https://registry.npmjs.org/concat-map/-/concat-map-0.0.1.tgz",
+      "integrity": "sha1-2Klr13/Wjfd5OnMDajug1UBdR3s=",
+      "dev": true
+    },
+    "console-browserify": {
+      "version": "1.1.0",
+      "resolved": "https://registry.npmjs.org/console-browserify/-/console-browserify-1.1.0.tgz",
+      "integrity": "sha1-8CQcRXMKn8YyOyBtvzjtx0HQuxA=",
+      "dev": true,
+      "requires": {
+        "date-now": "^0.1.4"
+      }
+    },
+    "core-util-is": {
+      "version": "1.0.2",
+      "resolved": "https://registry.npmjs.org/core-util-is/-/core-util-is-1.0.2.tgz",
+      "integrity": "sha1-tf1UIgqivFq1eqtxQMlAdUUDwac=",
+      "dev": true
+    },
+    "date-now": {
+      "version": "0.1.4",
+      "resolved": "https://registry.npmjs.org/date-now/-/date-now-0.1.4.tgz",
+      "integrity": "sha1-6vQ5/U1ISK105cx9vvIAZyueNFs=",
+      "dev": true
+    },
+    "deep-equal": {
+      "version": "0.0.0",
+      "resolved": "https://registry.npmjs.org/deep-equal/-/deep-equal-0.0.0.tgz",
+      "integrity": "sha1-mWedO70EcVb81FDT0B7rkGhpHoM=",
+      "dev": true
+    },
+    "deep-is": {
+      "version": "0.1.3",
+      "resolved": "https://registry.npmjs.org/deep-is/-/deep-is-0.1.3.tgz",
+      "integrity": "sha1-s2nW+128E+7PUk+RsHD+7cNXzzQ=",
+      "dev": true
+    },
+    "difflet": {
+      "version": "0.2.6",
+      "resolved": "https://registry.npmjs.org/difflet/-/difflet-0.2.6.tgz",
+      "integrity": "sha1-qyOzH1ZJtvqo49KsvTNEZzZcpvo=",
+      "dev": true,
+      "requires": {
+        "charm": "0.1.x",
+        "deep-is": "0.1.x",
+        "traverse": "0.6.x"
+      }
+    },
+    "dom-serializer": {
+      "version": "0.1.1",
+      "resolved": "https://registry.npmjs.org/dom-serializer/-/dom-serializer-0.1.1.tgz",
+      "integrity": "sha512-l0IU0pPzLWSHBcieZbpOKgkIn3ts3vAh7ZuFyXNwJxJXk/c4Gwj9xaTJwIDVQCXawWD0qb3IzMGH5rglQaO0XA==",
+      "dev": true,
+      "requires": {
+        "domelementtype": "^1.3.0",
+        "entities": "^1.1.1"
+      },
+      "dependencies": {
+        "entities": {
+          "version": "1.1.2",
+          "resolved": "https://registry.npmjs.org/entities/-/entities-1.1.2.tgz",
+          "integrity": "sha512-f2LZMYl1Fzu7YSBKg+RoROelpOaNrcGmE9AZubeDfrCEia483oW4MI4VyFd5VNHIgQ/7qm1I0wUHK1eJnn2y2w==",
+          "dev": true
+        }
+      }
+    },
+    "domelementtype": {
+      "version": "1.3.1",
+      "resolved": "https://registry.npmjs.org/domelementtype/-/domelementtype-1.3.1.tgz",
+      "integrity": "sha512-BSKB+TSpMpFI/HOxCNr1O8aMOTZ8hT3pM3GQ0w/mWRmkhEDSFJkkyzz4XQsBV44BChwGkrDfMyjVD0eA2aFV3w==",
+      "dev": true
+    },
+    "domhandler": {
+      "version": "2.3.0",
+      "resolved": "https://registry.npmjs.org/domhandler/-/domhandler-2.3.0.tgz",
+      "integrity": "sha1-LeWaCCLVAn+r/28DLCsloqir5zg=",
+      "dev": true,
+      "requires": {
+        "domelementtype": "1"
+      }
+    },
+    "domutils": {
+      "version": "1.5.1",
+      "resolved": "https://registry.npmjs.org/domutils/-/domutils-1.5.1.tgz",
+      "integrity": "sha1-3NhIiib1Y9YQeeSMn3t+Mjc2gs8=",
+      "dev": true,
+      "requires": {
+        "dom-serializer": "0",
+        "domelementtype": "1"
+      }
+    },
+    "entities": {
+      "version": "1.0.0",
+      "resolved": "https://registry.npmjs.org/entities/-/entities-1.0.0.tgz",
+      "integrity": "sha1-sph6o4ITR/zeZCsk/fyeT7cSvyY=",
+      "dev": true
+    },
+    "exit": {
+      "version": "0.1.2",
+      "resolved": "https://registry.npmjs.org/exit/-/exit-0.1.2.tgz",
+      "integrity": "sha1-BjJjj42HfMghB9MKD/8aF8uhzQw=",
+      "dev": true
+    },
+    "fs.realpath": {
+      "version": "1.0.0",
+      "resolved": "https://registry.npmjs.org/fs.realpath/-/fs.realpath-1.0.0.tgz",
+      "integrity": "sha1-FQStJSMVjKpA20onh8sBQRmU6k8=",
+      "dev": true
+    },
+    "glob": {
+      "version": "7.1.3",
+      "resolved": "https://registry.npmjs.org/glob/-/glob-7.1.3.tgz",
+      "integrity": "sha512-vcfuiIxogLV4DlGBHIUOwI0IbrJ8HWPc4MU7HzviGeNho/UJDfi6B5p3sHeWIQ0KGIU0Jpxi5ZHxemQfLkkAwQ==",
+      "dev": true,
+      "requires": {
+        "fs.realpath": "^1.0.0",
+        "inflight": "^1.0.4",
+        "inherits": "2",
+        "minimatch": "^3.0.4",
+        "once": "^1.3.0",
+        "path-is-absolute": "^1.0.0"
+      }
+    },
+    "htmlparser2": {
+      "version": "3.8.3",
+      "resolved": "https://registry.npmjs.org/htmlparser2/-/htmlparser2-3.8.3.tgz",
+      "integrity": "sha1-mWwosZFRaovoZQGn15dX5ccMEGg=",
+      "dev": true,
+      "requires": {
+        "domelementtype": "1",
+        "domhandler": "2.3",
+        "domutils": "1.5",
+        "entities": "1.0",
+        "readable-stream": "1.1"
+      }
+    },
+    "inflight": {
+      "version": "1.0.6",
+      "resolved": "https://registry.npmjs.org/inflight/-/inflight-1.0.6.tgz",
+      "integrity": "sha1-Sb1jMdfQLQwJvJEKEHW6gWW1bfk=",
+      "dev": true,
+      "requires": {
+        "once": "^1.3.0",
+        "wrappy": "1"
+      }
+    },
+    "inherits": {
+      "version": "2.0.3",
+      "resolved": "https://registry.npmjs.org/inherits/-/inherits-2.0.3.tgz",
+      "integrity": "sha1-Yzwsg+PaQqUC9SRmAiSA9CCCYd4=",
+      "dev": true
+    },
+    "isarray": {
+      "version": "0.0.1",
+      "resolved": "https://registry.npmjs.org/isarray/-/isarray-0.0.1.tgz",
+      "integrity": "sha1-ihis/Kmo9Bd+Cav8YDiTmwXR7t8=",
+      "dev": true
+    },
+    "jshint": {
+      "version": "2.10.2",
+      "resolved": "https://registry.npmjs.org/jshint/-/jshint-2.10.2.tgz",
+      "integrity": "sha512-e7KZgCSXMJxznE/4WULzybCMNXNAd/bf5TSrvVEq78Q/K8ZwFpmBqQeDtNiHc3l49nV4E/+YeHU/JZjSUIrLAA==",
+      "dev": true,
+      "requires": {
+        "cli": "~1.0.0",
+        "console-browserify": "1.1.x",
+        "exit": "0.1.x",
+        "htmlparser2": "3.8.x",
+        "lodash": "~4.17.11",
+        "minimatch": "~3.0.2",
+        "shelljs": "0.3.x",
+        "strip-json-comments": "1.0.x"
+      }
+    },
+    "lodash": {
+      "version": "4.17.11",
+      "resolved": "https://registry.npmjs.org/lodash/-/lodash-4.17.11.tgz",
+      "integrity": "sha512-cQKh8igo5QUhZ7lg38DYWAxMvjSAKG0A8wGSVimP07SIUEK2UO+arSRKbRZWtelMtN5V0Hkwh5ryOto/SshYIg==",
+      "dev": true
+    },
+    "lru-cache": {
+      "version": "2.7.3",
+      "resolved": "https://registry.npmjs.org/lru-cache/-/lru-cache-2.7.3.tgz",
+      "integrity": "sha1-bUUk6LlV+V1PW1iFHOId1y+06VI=",
+      "dev": true
+    },
+    "minimatch": {
+      "version": "3.0.4",
+      "resolved": "https://registry.npmjs.org/minimatch/-/minimatch-3.0.4.tgz",
+      "integrity": "sha512-yJHVQEhyqPLUTgt9B83PXu6W3rx4MvvHvSUvToogpwoGDOUQ+yDrR0HRot+yOCdCO7u4hX3pWft6kWBBcqh0UA==",
+      "dev": true,
+      "requires": {
+        "brace-expansion": "^1.1.7"
+      }
+    },
+    "minimist": {
+      "version": "0.0.8",
+      "resolved": "https://registry.npmjs.org/minimist/-/minimist-0.0.8.tgz",
+      "integrity": "sha1-hX/Kv8M5fSYluCKCYuhqp6ARsF0=",
+      "dev": true
+    },
+    "mkdirp": {
+      "version": "0.5.1",
+      "resolved": "https://registry.npmjs.org/mkdirp/-/mkdirp-0.5.1.tgz",
+      "integrity": "sha1-MAV0OOrGz3+MR2fzhkjWaX11yQM=",
+      "dev": true,
+      "requires": {
+        "minimist": "0.0.8"
+      }
+    },
+    "nopt": {
+      "version": "2.2.1",
+      "resolved": "https://registry.npmjs.org/nopt/-/nopt-2.2.1.tgz",
+      "integrity": "sha1-KqCbfRdoSHs7ianFqlIzW/8Lrqc=",
+      "dev": true,
+      "requires": {
+        "abbrev": "1"
+      }
+    },
+    "once": {
+      "version": "1.4.0",
+      "resolved": "https://registry.npmjs.org/once/-/once-1.4.0.tgz",
+      "integrity": "sha1-WDsap3WWHUsROsF9nFC6753Xa9E=",
+      "dev": true,
+      "requires": {
+        "wrappy": "1"
+      }
+    },
+    "path-is-absolute": {
+      "version": "1.0.1",
+      "resolved": "https://registry.npmjs.org/path-is-absolute/-/path-is-absolute-1.0.1.tgz",
+      "integrity": "sha1-F0uSaHNVNP+8es5r9TpanhtcX18=",
+      "dev": true
+    },
+    "readable-stream": {
+      "version": "1.1.14",
+      "resolved": "https://registry.npmjs.org/readable-stream/-/readable-stream-1.1.14.tgz",
+      "integrity": "sha1-fPTFTvZI44EwhMY23SB54WbAgdk=",
+      "dev": true,
+      "requires": {
+        "core-util-is": "~1.0.0",
+        "inherits": "~2.0.1",
+        "isarray": "0.0.1",
+        "string_decoder": "~0.10.x"
+      }
+    },
+    "runforcover": {
+      "version": "0.0.2",
+      "resolved": "https://registry.npmjs.org/runforcover/-/runforcover-0.0.2.tgz",
+      "integrity": "sha1-NE8FfY1F0zrrxsyCIEZ49pxIV8w=",
+      "dev": true,
+      "requires": {
+        "bunker": "0.1.X"
+      }
+    },
+    "shelljs": {
+      "version": "0.3.0",
+      "resolved": "https://registry.npmjs.org/shelljs/-/shelljs-0.3.0.tgz",
+      "integrity": "sha1-NZbmMHp4FUT1kfN9phg2DzHbV7E=",
+      "dev": true
+    },
+    "sigmund": {
+      "version": "1.0.1",
+      "resolved": "https://registry.npmjs.org/sigmund/-/sigmund-1.0.1.tgz",
+      "integrity": "sha1-P/IfGYytIXX587eBhT/ZTQ0ZtZA=",
+      "dev": true
+    },
+    "slide": {
+      "version": "1.1.6",
+      "resolved": "https://registry.npmjs.org/slide/-/slide-1.1.6.tgz",
+      "integrity": "sha1-VusCfWW00tzmyy4tMsTUr8nh1wc=",
+      "dev": true
+    },
+    "string_decoder": {
+      "version": "0.10.31",
+      "resolved": "https://registry.npmjs.org/string_decoder/-/string_decoder-0.10.31.tgz",
+      "integrity": "sha1-YuIDvEF2bGwoyfyEMB2rHFMQ+pQ=",
+      "dev": true
+    },
+    "strip-json-comments": {
+      "version": "1.0.4",
+      "resolved": "https://registry.npmjs.org/strip-json-comments/-/strip-json-comments-1.0.4.tgz",
+      "integrity": "sha1-HhX7ysl9Pumb8tc7TGVrCCu6+5E=",
+      "dev": true
+    },
+    "tap": {
+      "version": "0.4.13",
+      "resolved": "https://registry.npmjs.org/tap/-/tap-0.4.13.tgz",
+      "integrity": "sha1-OYYTTWdZcn/CIj5hEm7rhyQ6zLw=",
+      "dev": true,
+      "requires": {
+        "buffer-equal": "~0.0.0",
+        "deep-equal": "~0.0.0",
+        "difflet": "~0.2.0",
+        "glob": "~3.2.1",
+        "inherits": "*",
+        "mkdirp": "~0.3 || 0.4 || 0.5",
+        "nopt": "~2",
+        "runforcover": "~0.0.2",
+        "slide": "*",
+        "yamlish": "*"
+      },
+      "dependencies": {
+        "glob": {
+          "version": "3.2.11",
+          "resolved": "https://registry.npmjs.org/glob/-/glob-3.2.11.tgz",
+          "integrity": "sha1-Spc/Y1uRkPcV0QmH1cAP0oFevj0=",
+          "dev": true,
+          "requires": {
+            "inherits": "2",
+            "minimatch": "0.3"
+          }
+        },
+        "minimatch": {
+          "version": "0.3.0",
+          "resolved": "https://registry.npmjs.org/minimatch/-/minimatch-0.3.0.tgz",
+          "integrity": "sha1-J12O2qxPG7MyZHIInnlJyDlGmd0=",
+          "dev": true,
+          "requires": {
+            "lru-cache": "2",
+            "sigmund": "~1.0.0"
+          }
+        }
+      }
+    },
+    "traverse": {
+      "version": "0.6.6",
+      "resolved": "https://registry.npmjs.org/traverse/-/traverse-0.6.6.tgz",
+      "integrity": "sha1-y99WD9e5r2MlAv7UD5GMFX6pcTc=",
+      "dev": true
+    },
+    "uglify-js": {
+      "version": "1.1.1",
+      "resolved": "https://registry.npmjs.org/uglify-js/-/uglify-js-1.1.1.tgz",
+      "integrity": "sha1-7nGpfEzv0GoamyBDfzQRiYKqA1s=",
+      "dev": true
+    },
+    "wrappy": {
+      "version": "1.0.2",
+      "resolved": "https://registry.npmjs.org/wrappy/-/wrappy-1.0.2.tgz",
+      "integrity": "sha1-tSQ9jz7BqjXxNkYFvA0QNuMKtp8=",
+      "dev": true
+    },
+    "yamlish": {
+      "version": "0.0.7",
+      "resolved": "https://registry.npmjs.org/yamlish/-/yamlish-0.0.7.tgz",
+      "integrity": "sha1-tK+aHcxjYYhzw9bkUewyE8OaV/s=",
+      "dev": true
+    }
+  }
+}
diff --git a/package.json b/package.json
index 0350743..a778651 100644
--- a/package.json
+++ b/package.json
@@ -23,7 +23,7 @@
     "test": "make test"
   },
   "devDependencies": {
-    "tap": "~0.4.3",
-    "jshint": "~2.1.4"
+    "jshint": "^2.10.2",
+    "tap": "~0.4.3"
   }
 }
diff --git a/test/is_uri.js b/test/is_uri.js
index 5ac90a0..60296fa 100644
--- a/test/is_uri.js
+++ b/test/is_uri.js
@@ -16,6 +16,9 @@ test("testing is_uri", function (t) {
     t.ok(is_uri('tel:+1-816-555-1212'), 'tel:+1-816-555-1212');
     t.ok(is_uri('telnet://192.0.2.16:80/'), 'telnet://192.0.2.16:80/');
     t.ok(is_uri('urn:oasis:names:specification:docbook:dtd:xml:4.1.2'), 'urn:oasis:names:specification:docbook:dtd:xml:4.1.2');
+    t.ok(is_uri('//example.w3.org'), '//example.w3.org');
+    t.ok(is_uri('//example'), '//example');
+    t.ok(is_uri('http:/172.0.0.1:80/'), 'http://172.0.0.1:80/');
 
 
     // invalid