diff --git a/CHANGELOG.md b/CHANGELOG.md
index a5c509a..891a8cd 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -8,6 +8,9 @@ and this project adheres to [Semantic Versioning](http://semver.org/).
 <!-- ## Unreleased -->
 <!-- New PRs should document their changes here. -->
 
+## [2.1.1] - 2018-05-02
+* Updated dependencies and type definitions.
+
 ## [2.1.0] - 2018-03-07
 * Updated dependencies.
 * Convert to TypeScript.
diff --git a/package-lock.json b/package-lock.json
index 0b8e33c..d33ae94 100644
--- a/package-lock.json
+++ b/package-lock.json
@@ -5,9 +5,9 @@
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+      "version": "4.1.3",
+      "resolved": "https://registry.npmjs.org/@types/chai/-/chai-4.1.3.tgz",
+      "integrity": "sha512-f5dXGzOJycyzSMdaXVhiBhauL4dYydXwVpavfQ1mVCaGjR56a9QfklXObUxlIY9bGTmCPHEEZ04I16BZ/8w5ww==",
       "dev": true
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@@ -17,16 +17,16 @@
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-      "resolved": "https://registry.npmjs.org/@types/node/-/node-6.0.88.tgz",
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+      "version": "10.0.3",
+      "resolved": "https://registry.npmjs.org/@types/node/-/node-10.0.3.tgz",
+      "integrity": "sha512-J7nx6JzxmtT4zyvfLipYL7jNaxvlCWpyG7JhhCQ4fQyG+AGfovAHoYR55TFx+X8akfkUJYpt5JG6GPeFMjZaCQ=="
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       "integrity": "sha1-44cKEOgnNacg9i1x3NGDunjvOp0=",
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-        "@types/node": "6.0.88"
+        "@types/node": "10.0.3"
       }
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@@ -35,13 +35,13 @@
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       "dev": true,
       "requires": {
-        "@types/node": "6.0.88"
+        "@types/node": "10.0.3"
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-      "resolved": "https://registry.npmjs.org/acorn/-/acorn-5.1.2.tgz",
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+      "resolved": "https://registry.npmjs.org/acorn/-/acorn-5.5.3.tgz",
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@@ -62,21 +62,21 @@
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-      "integrity": "sha1-wG9Zh3jETGsWGrr+NGa4GtGBTtI=",
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+      "resolved": "https://registry.npmjs.org/ajv/-/ajv-5.5.2.tgz",
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-        "fast-deep-equal": "1.0.0",
-        "json-schema-traverse": "0.3.1",
-        "json-stable-stringify": "1.0.1"
+        "fast-deep-equal": "1.1.0",
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-      "resolved": "https://registry.npmjs.org/ajv-keywords/-/ajv-keywords-2.1.0.tgz",
-      "integrity": "sha1-opbhf3v658HOT34N5T0pyzIWLfA=",
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@@ -88,9 +88,9 @@
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+      "version": "3.1.0",
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@@ -106,9 +106,9 @@
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-      "integrity": "sha1-c9g7wmP4bpf4zE9rrhsOkKfSLIY=",
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@@ -144,9 +144,9 @@
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-      "integrity": "sha1-E8pRXYYgbaC6xm6DTdOX2HWBCUw=",
+      "version": "1.1.0",
+      "resolved": "https://registry.npmjs.org/assertion-error/-/assertion-error-1.1.0.tgz",
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@@ -191,9 +191,9 @@
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-      "integrity": "sha1-wHshHHyVLsH479Uad+8NHTmQopI=",
+      "version": "1.1.11",
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@@ -201,9 +201,15 @@
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@@ -233,45 +239,51 @@
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           "dev": true,
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+            "has-flag": "3.0.0"
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@@ -317,14 +329,14 @@
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@@ -354,7 +366,7 @@
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@@ -366,7 +378,7 @@
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+        "ajv": "5.5.2",
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-        "ignore": "3.3.5",
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@@ -529,23 +541,13 @@
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@@ -1245,15 +1256,21 @@
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+      "dev": true
+    },
+    "safer-buffer": {
+      "version": "2.1.2",
+      "resolved": "https://registry.npmjs.org/safer-buffer/-/safer-buffer-2.1.2.tgz",
+      "integrity": "sha512-YZo3K82SD7Riyi0E1EQPojLz7kpepnSQI9IyPbHHg1XXXevb5dJI7tpyN2ADxGcQbHG7vcyRHk0cbwqcQriUtg==",
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     "semver": {
-      "version": "5.4.1",
-      "resolved": "https://registry.npmjs.org/semver/-/semver-5.4.1.tgz",
-      "integrity": "sha512-WfG/X9+oATh81XtllIo/I8gOiY9EXRdv1cQdyykeXK17YcUW3EXUAi2To4pcH6nZtJPr7ZOpM5OMyWJZm+8Rsg==",
+      "version": "5.5.0",
+      "resolved": "https://registry.npmjs.org/semver/-/semver-5.5.0.tgz",
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@@ -1308,12 +1325,12 @@
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+      "resolved": "https://registry.npmjs.org/string_decoder/-/string_decoder-1.1.1.tgz",
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       "dev": true,
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-        "safe-buffer": "5.1.1"
+        "safe-buffer": "5.1.2"
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@@ -1351,10 +1368,10 @@
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-        "ajv": "5.2.3",
-        "ajv-keywords": "2.1.0",
-        "chalk": "2.1.0",
-        "lodash": "4.17.4",
+        "ajv": "5.5.2",
+        "ajv-keywords": "2.1.1",
+        "chalk": "2.4.1",
+        "lodash": "4.17.10",
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@@ -1365,9 +1382,9 @@
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       "requires": {
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-        "core-js": "2.5.1",
+        "core-js": "2.5.5",
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-        "feature-detect-es6": "1.3.1",
+        "feature-detect-es6": "1.4.0",
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@@ -1393,16 +1410,6 @@
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-    "through2": {
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@@ -1412,12 +1419,6 @@
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@@ -1432,65 +1433,30 @@
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-        "commander": "2.14.1",
-        "diff": "3.3.1",
+        "chalk": "2.4.1",
+        "commander": "2.15.1",
+        "diff": "3.5.0",
         "glob": "7.1.2",
-        "js-yaml": "3.10.0",
+        "js-yaml": "3.11.0",
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-        "resolve": "1.5.0",
-        "semver": "5.4.1",
+        "resolve": "1.7.1",
+        "semver": "5.5.0",
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-        "tsutils": "2.21.2"
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-            "escape-string-regexp": "1.0.5",
-            "supports-color": "5.2.0"
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-          "resolved": "https://registry.npmjs.org/commander/-/commander-2.14.1.tgz",
-          "integrity": "sha512-+YR16o3rK53SmWHU3rEM3tPAh2rwb1yPcQX5irVn7mb0gXbwuCCrnkbV5+PBfETdfg1vui07nM6PCG1zndcjQw==",
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-          "resolved": "https://registry.npmjs.org/has-flag/-/has-flag-3.0.0.tgz",
-          "integrity": "sha1-tdRU3CGZriJWmfNGfloH87lVuv0=",
+          "version": "2.15.1",
+          "resolved": "https://registry.npmjs.org/commander/-/commander-2.15.1.tgz",
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-          "resolved": "https://registry.npmjs.org/supports-color/-/supports-color-5.2.0.tgz",
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-          "dev": true,
-          "requires": {
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     "tsutils": {
-      "version": "2.21.2",
-      "resolved": "https://registry.npmjs.org/tsutils/-/tsutils-2.21.2.tgz",
-      "integrity": "sha512-iaIuyjIUeFLdD39MYdzqBuY7Zv6+uGxSwRH4mf+HuzsnznjFz0R2tGrAe0/JvtNh91WrN8UN/DZRFTZNDuVekA==",
+      "version": "2.26.2",
+      "resolved": "https://registry.npmjs.org/tsutils/-/tsutils-2.26.2.tgz",
+      "integrity": "sha512-uzwnhmrSbyinPCiwfzGsOY3IulBTwoky7r83HmZdz9QNCjhSCzavkh47KLWuU0zF2F2WbpmmzoJUIEiYyd+jEQ==",
       "dev": true,
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@@ -1506,9 +1472,9 @@
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-      "version": "4.0.3",
-      "resolved": "https://registry.npmjs.org/type-detect/-/type-detect-4.0.3.tgz",
-      "integrity": "sha1-Dj8mcLRAmbC0bChNE2p+9Jx0wuo=",
+      "version": "4.0.8",
+      "resolved": "https://registry.npmjs.org/type-detect/-/type-detect-4.0.8.tgz",
+      "integrity": "sha512-0fr/mIH1dlO+x7TlcMy+bIDqKPsw/70tVyeHW787goQjhmqaZe10uwLujubK9q9Lg6Fiho1KUKDYz0Z7k7g5/g==",
       "dev": true
     },
     "typedarray": {
@@ -1518,9 +1484,9 @@
       "dev": true
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     "typescript": {
-      "version": "2.7.2",
-      "resolved": "https://registry.npmjs.org/typescript/-/typescript-2.7.2.tgz",
-      "integrity": "sha512-p5TCYZDAO0m4G344hD+wx/LATebLWZNkkh2asWUFqSsD2OrDNhbAHuSjobrmsUmdzjJjEeZVU9g1h3O6vpstnw==",
+      "version": "2.8.3",
+      "resolved": "https://registry.npmjs.org/typescript/-/typescript-2.8.3.tgz",
+      "integrity": "sha512-K7g15Bb6Ra4lKf7Iq2l/I5/En+hLIHmxWZGq3D4DIRNFxMNV6j2SHSvDOqs2tGd4UvD/fJvrwopzQXjLrT7Itw==",
       "dev": true
     },
     "typical": {
@@ -1543,7 +1509,7 @@
         "clone": "2.1.1",
         "clone-buffer": "1.0.0",
         "clone-stats": "1.0.0",
-        "cloneable-readable": "1.0.0",
+        "cloneable-readable": "1.1.2",
         "remove-trailing-separator": "1.1.0",
         "replace-ext": "1.0.0"
       }
@@ -1569,7 +1535,7 @@
       "integrity": "sha1-q1X2leYRjak4WP3XDAU9HF4BrCA=",
       "requires": {
         "array-back": "1.0.4",
-        "feature-detect-es6": "1.3.1",
+        "feature-detect-es6": "1.4.0",
         "reduce-flatten": "1.0.1",
         "typical": "2.6.1"
       }
@@ -1589,12 +1555,6 @@
         "mkdirp": "0.5.1"
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-    "xtend": {
-      "version": "4.0.1",
-      "resolved": "https://registry.npmjs.org/xtend/-/xtend-4.0.1.tgz",
-      "integrity": "sha1-pcbVMr5lbiPbgg77lDofBJmNY68=",
-      "dev": true
-    },
     "yallist": {
       "version": "2.1.2",
       "resolved": "https://registry.npmjs.org/yallist/-/yallist-2.1.2.tgz",
diff --git a/package.json b/package.json
index 0646404..100cdf0 100644
--- a/package.json
+++ b/package.json
@@ -24,7 +24,7 @@
     "eslint": "^4.8.0",
     "mocha": "^5.0.1",
     "tslint": "^5.9.1",
-    "typescript": "^2.7.2",
+    "typescript": "^2.8.3",
     "vinyl": "^2.1.0"
   },
   "engines": {
diff --git a/src/index.ts b/src/index.ts
index bb2b953..190b68a 100644
--- a/src/index.ts
+++ b/src/index.ts
@@ -66,7 +66,7 @@ export class GulpTransform extends stream.Transform {
     super({objectMode: true});
   }
   _transform(file: vinyl, _encoding: string,
-             callback: (error: Error|null|undefined, file?: vinyl) => void) {
+             callback: (error?: Error, file?: vinyl) => void) {
     if (file.isStream()) {
       return callback(new Error('css-slam does not support streams'));
     }
@@ -80,7 +80,7 @@ export class GulpTransform extends stream.Transform {
         file.contents = new Buffer(css(contents));
       }
     }
-    callback(null, file);
+    callback(undefined, file);
   }
 }