diff --git a/src/core/operations/Gunzip.mjs b/src/core/operations/Gunzip.mjs
index 07b1d6c2..ef487b06 100644
--- a/src/core/operations/Gunzip.mjs
+++ b/src/core/operations/Gunzip.mjs
@@ -5,9 +5,9 @@
  */
 
 import Operation from "../Operation.mjs";
-import zlibAndGzip from "zlibjs/bin/zlib_and_gzip.min.js";
+import gunzip from "zlibjs/bin/gunzip.min.js";
 
-const Zlib = zlibAndGzip.Zlib;
+const Zlib = gunzip.Zlib;
 
 /**
  * Gunzip operation
@@ -42,8 +42,8 @@ class Gunzip extends Operation {
      * @returns {File}
      */
     run(input, args) {
-        const gunzip = new Zlib.Gunzip(new Uint8Array(input));
-        return new Uint8Array(gunzip.decompress()).buffer;
+        const gzipObj = new Zlib.Gunzip(new Uint8Array(input));
+        return new Uint8Array(gzipObj.decompress()).buffer;
     }
 
 }
diff --git a/src/core/operations/Gzip.mjs b/src/core/operations/Gzip.mjs
index 5f9fa474..093ae6a4 100644
--- a/src/core/operations/Gzip.mjs
+++ b/src/core/operations/Gzip.mjs
@@ -6,9 +6,9 @@
 
 import Operation from "../Operation.mjs";
 import {COMPRESSION_TYPE, ZLIB_COMPRESSION_TYPE_LOOKUP} from "../lib/Zlib.mjs";
-import zlibAndGzip from "zlibjs/bin/zlib_and_gzip.min.js";
+import gzip from "zlibjs/bin/gzip.min.js";
 
-const Zlib = zlibAndGzip.Zlib;
+const Zlib = gzip.Zlib;
 
 /**
  * Gzip operation
@@ -73,12 +73,15 @@ class Gzip extends Operation {
             options.filename = filename;
         }
         if (comment.length) {
-            options.flags.fcommenct = true;
+            options.flags.comment = true;
             options.comment = comment;
         }
-
-        const gzip = new Zlib.Gzip(new Uint8Array(input), options);
-        return new Uint8Array(gzip.compress()).buffer;
+        const gzipObj = new Zlib.Gzip(new Uint8Array(input), options);
+        const compressed = new Uint8Array(gzipObj.compress());
+        if (options.flags.comment && !(compressed[3] & 0x10)) {
+            compressed[3] |= 0x10;
+        }
+        return compressed.buffer;
     }
 
 }
diff --git a/tests/operations/index.mjs b/tests/operations/index.mjs
index c54fa7ef..51676386 100644
--- a/tests/operations/index.mjs
+++ b/tests/operations/index.mjs
@@ -41,6 +41,8 @@ import "./tests/DateTime.mjs";
 import "./tests/ExtractEmailAddresses.mjs";
 import "./tests/Fork.mjs";
 import "./tests/FromDecimal.mjs";
+import "./tests/Gzip.mjs";
+import "./tests/Gunzip.mjs";
 import "./tests/Hash.mjs";
 import "./tests/HaversineDistance.mjs";
 import "./tests/Hexdump.mjs";
diff --git a/tests/operations/tests/Gunzip.mjs b/tests/operations/tests/Gunzip.mjs
new file mode 100644
index 00000000..70b67a31
--- /dev/null
+++ b/tests/operations/tests/Gunzip.mjs
@@ -0,0 +1,58 @@
+/**
+ * Gunzip Tests.
+ *
+ * @author n1073645 [n1073645@gmail.com]
+ *
+ * @copyright Crown Copyright 2019
+ * @license Apache-2.0
+ */
+
+import TestRegister from "../../lib/TestRegister.mjs";
+
+TestRegister.addTests([
+    {
+        name: "Gunzip: No comment, no checksum and no filename",
+        input: "1f8b0800f7c8f85d00ff0dc9dd0180200804e0556ea8262848fb3dc588c6a7e76faa8aeedb726036c68d951f76bf9a0af8aae1f97d9c0c084b02509cbf8c2c000000",
+        expectedOutput: "The quick brown fox jumped over the slow dog",
+        recipeConfig: [
+            {
+                op: "From Hex",
+                args: ["None"]
+            },
+            {
+                op: "Gunzip",
+                args: []
+            }
+        ]
+    },
+    {
+        name: "Gunzip: No comment, no checksum and filename",
+        input: "1f8b080843c9f85d00ff66696c656e616d65000dc9dd0180200804e0556ea8262848fb3dc588c6a7e76faa8aeedb726036c68d951f76bf9a0af8aae1f97d9c0c084b02509cbf8c2c000000",
+        expectedOutput: "The quick brown fox jumped over the slow dog",
+        recipeConfig: [
+            {
+                op: "From Hex",
+                args: ["None"]
+            },
+            {
+                op: "Gunzip",
+                args: []
+            }
+        ]
+    },
+    {
+        name: "Gunzip: Has a comment, no checksum and has a filename",
+        input: "1f8b08186fc9f85d00ff66696c656e616d6500636f6d6d656e74000dc9dd0180200804e0556ea8262848fb3dc588c6a7e76faa8aeedb726036c68d951f76bf9a0af8aae1f97d9c0c084b02509cbf8c2c000000",
+        expectedOutput: "The quick brown fox jumped over the slow dog",
+        recipeConfig: [
+            {
+                op: "From Hex",
+                args: ["None"]
+            },
+            {
+                op: "Gunzip",
+                args: []
+            }
+        ]
+    }
+]);
diff --git a/tests/operations/tests/Gzip.mjs b/tests/operations/tests/Gzip.mjs
new file mode 100644
index 00000000..c9b2b8ca
--- /dev/null
+++ b/tests/operations/tests/Gzip.mjs
@@ -0,0 +1,89 @@
+/**
+ * Gzip Tests.
+ *
+ * @author n1073645 [n1073645@gmail.com]
+ *
+ * @copyright Crown Copyright 2019
+ * @license Apache-2.0
+ */
+
+import TestRegister from "../../lib/TestRegister.mjs";
+
+TestRegister.addTests([
+    {
+        name: "Gzip: No comment, no checksum and no filename",
+        input: "The quick brown fox jumped over the slow dog",
+        expectedOutput: "0dc9dd0180200804e0556ea8262848fb3dc588c6a7e76faa8aeedb726036c68d951f76bf9a0af8aae1f97d9c0c084b02509cbf8c2c000000",
+        recipeConfig: [
+            {
+                op: "Gzip",
+                args: ["Dynamic Huffman Coding", "", "", false]
+            },
+            {
+                op: "Drop bytes",
+                args: [0, 10, false]
+            },
+            {
+                op: "To Hex",
+                args: ["None"]
+            }
+        ]
+    },
+    {
+        name: "Gzip: No comment, no checksum and has a filename",
+        input: "The quick brown fox jumped over the slow dog",
+        expectedOutput: "636f6d6d656e74000dc9dd0180200804e0556ea8262848fb3dc588c6a7e76faa8aeedb726036c68d951f76bf9a0af8aae1f97d9c0c084b02509cbf8c2c000000",
+        recipeConfig: [
+            {
+                op: "Gzip",
+                args: ["Dynamic Huffman Coding", "comment", "", false]
+            },
+            {
+                op: "Drop bytes",
+                args: [0, 10, false]
+            },
+            {
+                op: "To Hex",
+                args: ["None"]
+            }
+        ]
+    },
+    {
+        name: "Gzip: Has a comment, no checksum and no filename",
+        input: "The quick brown fox jumped over the slow dog",
+        expectedOutput: "636f6d6d656e74000dc9dd0180200804e0556ea8262848fb3dc588c6a7e76faa8aeedb726036c68d951f76bf9a0af8aae1f97d9c0c084b02509cbf8c2c000000",
+        recipeConfig: [
+            {
+                op: "Gzip",
+                args: ["Dynamic Huffman Coding", "", "comment", false]
+            },
+            {
+                op: "Drop bytes",
+                args: [0, 10, false]
+            },
+            {
+                op: "To Hex",
+                args: ["None"]
+            }
+        ]
+    },
+    {
+        name: "Gzip: Has a comment, no checksum and has a filename",
+        input: "The quick brown fox jumped over the slow dog",
+        expectedOutput: "66696c656e616d6500636f6d6d656e74000dc9dd0180200804e0556ea8262848fb3dc588c6a7e76faa8aeedb726036c68d951f76bf9a0af8aae1f97d9c0c084b02509cbf8c2c000000",
+        recipeConfig: [
+            {
+                op: "Gzip",
+                args: ["Dynamic Huffman Coding", "filename", "comment", false]
+            },
+            {
+                op: "Drop bytes",
+                args: [0, 10, false]
+            },
+            {
+                op: "To Hex",
+                args: ["None"]
+            }
+        ]
+    },
+]);