diff --git a/src/tables/cff.mjs b/src/tables/cff.mjs
index b189c289..7f4d3d0d 100755
--- a/src/tables/cff.mjs
+++ b/src/tables/cff.mjs
@@ -308,6 +308,17 @@ function interpretDict(dict, meta, strings) {
             if (m.type === 'SID') {
                 value = getCFFString(strings, value);
             }
+            if (m.type === 'delta' && value !== null) {
+                if (!Array.isArray(value) || value.length % 2 != 0) {
+                    throw new Error(`Read delta data invalid`);
+                }
+                // Convert delta array to human readable version
+                let current = 0;
+                for(let i = 0; i < value.length; i++) {
+                    value[i] = value[i] + current;
+                    current = value[i]
+                }
+            }
             newDict[m.name] = value;
         }
     }
@@ -1416,6 +1427,21 @@ function makeDict(meta, attrs, strings) {
             if (entry.type === 'SID') {
                 value = encodeString(value, strings);
             }
+            if (entry.type === 'delta' && value !== null) {
+                if (!Array.isArray(value) || value.length % 2 != 0) {
+                    throw new Error(`Provided delta data invalid`);
+                }
+                // Convert human readable delta array to DICT version
+                // See https://adobe-type-tools.github.io/font-tech-notes/pdfs/5176.CFF.pdf
+                // Private DICT data > Table 6 Operand Types > delta
+                let current = 0;
+                for(let i = 0; i < value.length; i++) {
+                    let nextcurrent = value[i];
+                    value[i] = value[i] - current;
+                    current = nextcurrent;
+                }
+		    console.log("OUTCOMING", value);
+            }
 
             m[entry.op] = {name: entry.name, type: entry.type, value: value};
         }
diff --git a/test/tables/cff.spec.mjs b/test/tables/cff.spec.mjs
index ab46f19e..b4e4690a 100644
--- a/test/tables/cff.spec.mjs
+++ b/test/tables/cff.spec.mjs
@@ -93,10 +93,10 @@ describe('tables/cff.mjs', function () {
         assert.equal(topDict.vstore, 16);
         assert.equal(topDict.fdSelect, null);
 
-        assert.deepEqual(privateDict1.blueValues, [-20, 20, 472, 18, 35, 15, 105, 15, 10, 20, 40, 20]);
-        assert.deepEqual(privateDict1.otherBlues, [-250, 10]);
-        assert.deepEqual(privateDict1.familyBlues, [-20, 20, 473, 18, 34, 15, 104, 15, 10, 20, 40, 20]);
-        assert.deepEqual(privateDict1.familyOtherBlues, [ -249, 10 ]);
+        assert.deepEqual(privateDict1.blueValues, [-20, 0, 472, 490, 525, 540, 645, 660, 670, 690, 730, 750]);
+        assert.deepEqual(privateDict1.otherBlues, [-250, -240]);
+        assert.deepEqual(privateDict1.familyBlues, [-20, 0, 473, 491, 525, 540, 644, 659, 669, 689, 729, 749]);
+        assert.deepEqual(privateDict1.familyOtherBlues, [ -249, -239 ]);
         assert.equal(privateDict1.blueScale, 0.0375);
         assert.equal(privateDict1.blueShift, 7);
         assert.equal(privateDict1.blueFuzz, 0);