diff --git a/src/core/operations/FromDecimal.mjs b/src/core/operations/FromDecimal.mjs
index f3c117ff..1d0f272c 100644
--- a/src/core/operations/FromDecimal.mjs
+++ b/src/core/operations/FromDecimal.mjs
@@ -29,38 +29,43 @@ class FromDecimal extends Operation {
                 "name": "Delimiter",
                 "type": "option",
                 "value": DELIM_OPTIONS
+            },
+            {
+                "name": "Support signed values",
+                "type": "boolean",
+                "value": false
             }
         ];
         this.patterns = [
             {
                 match: "^(?:\\d{1,2}|1\\d{2}|2[0-4]\\d|25[0-5])(?: (?:\\d{1,2}|1\\d{2}|2[0-4]\\d|25[0-5]))*$",
                 flags: "",
-                args: ["Space"]
+                args: ["Space", false]
             },
             {
                 match: "^(?:\\d{1,2}|1\\d{2}|2[0-4]\\d|25[0-5])(?:,(?:\\d{1,2}|1\\d{2}|2[0-4]\\d|25[0-5]))*$",
                 flags: "",
-                args: ["Comma"]
+                args: ["Comma", false]
             },
             {
                 match: "^(?:\\d{1,2}|1\\d{2}|2[0-4]\\d|25[0-5])(?:;(?:\\d{1,2}|1\\d{2}|2[0-4]\\d|25[0-5]))*$",
                 flags: "",
-                args: ["Semi-colon"]
+                args: ["Semi-colon", false]
             },
             {
                 match: "^(?:\\d{1,2}|1\\d{2}|2[0-4]\\d|25[0-5])(?::(?:\\d{1,2}|1\\d{2}|2[0-4]\\d|25[0-5]))*$",
                 flags: "",
-                args: ["Colon"]
+                args: ["Colon", false]
             },
             {
                 match: "^(?:\\d{1,2}|1\\d{2}|2[0-4]\\d|25[0-5])(?:\\n(?:\\d{1,2}|1\\d{2}|2[0-4]\\d|25[0-5]))*$",
                 flags: "",
-                args: ["Line feed"]
+                args: ["Line feed", false]
             },
             {
                 match: "^(?:\\d{1,2}|1\\d{2}|2[0-4]\\d|25[0-5])(?:\\r\\n(?:\\d{1,2}|1\\d{2}|2[0-4]\\d|25[0-5]))*$",
                 flags: "",
-                args: ["CRLF"]
+                args: ["CRLF", false]
             },
         ];
     }
@@ -71,7 +76,11 @@ class FromDecimal extends Operation {
      * @returns {byteArray}
      */
     run(input, args) {
-        return fromDecimal(input, args[0]);
+        let data = fromDecimal(input, args[0]);
+        if (args[1]) { // Convert negatives
+            data = data.map(v => v < 0 ? 0xFF + v + 1 : v);
+        }
+        return data;
     }
 
 }
diff --git a/src/core/operations/ToDecimal.mjs b/src/core/operations/ToDecimal.mjs
index cad8dc18..6df51ae2 100644
--- a/src/core/operations/ToDecimal.mjs
+++ b/src/core/operations/ToDecimal.mjs
@@ -30,6 +30,11 @@ class ToDecimal extends Operation {
                 "name": "Delimiter",
                 "type": "option",
                 "value": DELIM_OPTIONS
+            },
+            {
+                "name": "Support signed values",
+                "type": "boolean",
+                "value": false
             }
         ];
     }
@@ -40,7 +45,11 @@ class ToDecimal extends Operation {
      * @returns {string}
      */
     run(input, args) {
-        const delim = Utils.charRep(args[0]);
+        const delim = Utils.charRep(args[0]),
+            signed = args[1];
+        if (signed) {
+            input = input.map(v => v > 0x7F ? v - 0xFF - 1 : v);
+        }
         return input.join(delim);
     }
 
diff --git a/test/index.mjs b/test/index.mjs
index adf5144a..7d60618e 100644
--- a/test/index.mjs
+++ b/test/index.mjs
@@ -42,7 +42,8 @@ import "./tests/operations/Crypt";
 import "./tests/operations/DateTime";
 import "./tests/operations/ExtractEmailAddresses";
 import "./tests/operations/Fork";
-import "./tests/operations/FromGeohash.mjs";
+import "./tests/operations/FromDecimal";
+import "./tests/operations/FromGeohash";
 import "./tests/operations/Hash";
 import "./tests/operations/HaversineDistance";
 import "./tests/operations/Hexdump";
diff --git a/test/tests/operations/FromDecimal.mjs b/test/tests/operations/FromDecimal.mjs
new file mode 100644
index 00000000..b73292a8
--- /dev/null
+++ b/test/tests/operations/FromDecimal.mjs
@@ -0,0 +1,33 @@
+/**
+ * From Decimal tests
+ *
+ * @author qistoph
+ * @copyright Crown Copyright 2018
+ * @licence Apache-2.0
+ */
+import TestRegister from "../../TestRegister";
+
+TestRegister.addTests([
+    {
+        name: "From Decimal",
+        input: "83 97 109 112 108 101 32 84 101 120 116",
+        expectedOutput: "Sample Text",
+        recipeConfig: [
+            {
+                op: "From Decimal",
+                args: ["Space", false]
+            },
+        ],
+    },
+    {
+        name: "From Decimal with negatives",
+        input: "-130,-140,-152,-151,115,33,0,-1",
+        expectedOutput: "~this!\u0000\u00ff",
+        recipeConfig: [
+            {
+                op: "From Decimal",
+                args: ["Comma", true]
+            },
+        ],
+    },
+]);