diff --git a/lib/union.js b/lib/union.js
index 5f207ac..5ee6726 100644
--- a/lib/union.js
+++ b/lib/union.js
@@ -64,7 +64,7 @@ function Union () {
 
   UnionType.defineProperty = defineProperty
   UnionType.toString = toString
-  UnionType.fields = {}
+  UnionType.allFields = {}
 
   // comply with ref's "type" interface
   UnionType.size = 0
@@ -73,7 +73,7 @@ function Union () {
   UnionType.get = get
   UnionType.set = set
 
-  // Read the fields list
+  // Read the allFields list
   var arg = arguments[0]
   if (typeof arg === 'object') {
     Object.keys(arg).forEach(function (name) {
@@ -102,7 +102,7 @@ function set (buffer, offset, value) {
   var isUnion = value instanceof this
   if (isUnion) {
     // TODO: optimize - use Buffer#copy()
-    Object.keys(this.fields).forEach(function (name) {
+    Object.keys(this.allFields).forEach(function (name) {
       // hopefully hit the setters
       union[name] = value[name]
     })
@@ -151,7 +151,7 @@ function defineProperty (name, type) {
   var field = {
     type: type
   }
-  this.fields[name] = field
+  this.allFields[name] = field
 
   // calculate the new size and alignment
   recalc(this);
@@ -168,33 +168,34 @@ function defineProperty (name, type) {
 }
 
 function recalc (union) {
-  // reset size and alignment
-  union.size = 0
-  union.alignment = 0
+  var biggest
+  var fieldNames = Object.keys(union.allFields)
 
-  var fieldNames = Object.keys(union.fields)
-
-  // loop through to set the size of the union of the largest member field
-  // and the alignment to the requirements of the largest member
+  // find the largest member field by size / alignment
   fieldNames.forEach(function (name) {
-    var field = union.fields[name]
+    var field = union.allFields[name]
     var type = field.type
-
+    
     var size = type.indirection === 1 ? type.size : ref.sizeof.pointer
     var alignment = type.alignment || ref.alignof.pointer
     if (type.indirection > 1) {
       alignment = ref.alignof.pointer
     }
-    union.alignment = Math.max(union.alignment, alignment)
-    union.size = Math.max(union.size, size)
+    var fields = {}
+    fields[name] = { type: type }
+
+    var current = { fields: fields, size: size, alignment: alignment }
+
+    if (!biggest || size > biggest.size || alignment > biggest.alignment) {
+      biggest = current
+    }
   })
 
-  // any padding
-  var left = union.size % union.alignment
-  if (left > 0) {
-    debug('additional padding to the end of union:', union.alignment - left)
-    union.size += union.alignment - left
-  }
+  union.alignment = biggest.alignment;
+  union.size = biggest.size;
+  // Pretend like we only have this one field so that
+  // ffi-napi doesn't overcount the size
+  union.fields = biggest.fields;
 }
 
 
diff --git a/package-lock.json b/package-lock.json
index 269e09a..a3b31a0 100644
--- a/package-lock.json
+++ b/package-lock.json
@@ -1,18 +1,18 @@
 {
   "name": "@napi-ffi/ref-union-di",
-  "version": "1.0.1",
+  "version": "1.0.2",
   "lockfileVersion": 3,
   "requires": true,
   "packages": {
     "": {
       "name": "@napi-ffi/ref-union-di",
-      "version": "1.0.1",
+      "version": "1.0.2",
       "license": "MIT",
       "dependencies": {
         "debug": "^4.3.7"
       },
       "devDependencies": {
-        "@napi-ffi/ref-napi": "^3.0.5",
+        "@napi-ffi/ref-napi": "^3.0.7",
         "@napi-ffi/ref-struct-di": "^1.1.1",
         "mocha": "^7.1.1",
         "node-addon-api": "^8.2.1",
@@ -426,9 +426,9 @@
       }
     },
     "node_modules/@napi-ffi/ref-napi": {
-      "version": "3.0.5",
-      "resolved": "https://registry.npmjs.org/@napi-ffi/ref-napi/-/ref-napi-3.0.5.tgz",
-      "integrity": "sha512-Oxmr7OUyZpEu0m3eEjHuTOPqnDmAPZPAZcLAfhxhKf7a2mQV2/t0DwCMgx+QDpZLBiFZRHy7oba9fvWEXS469w==",
+      "version": "3.0.7",
+      "resolved": "https://registry.npmjs.org/@napi-ffi/ref-napi/-/ref-napi-3.0.7.tgz",
+      "integrity": "sha512-oCaKehZERf2mEnqTJnxv/2hNDT5CpCH3s4jqncbi8jfSp40ydjhWk/xkuBz3GuSoCWeMW2y3EvFQS+sNDrfnug==",
       "dev": true,
       "hasInstallScript": true,
       "license": "MIT",
diff --git a/package.json b/package.json
index 6f3c3bb..b3ceaf3 100644
--- a/package.json
+++ b/package.json
@@ -9,7 +9,7 @@
     "c++",
     "ffi"
   ],
-  "version": "1.0.1",
+  "version": "1.0.2",
   "author": "Anna Henningsen <anna@addaleax.net>",
   "contributors": [
     "Nathan Rajlich <nathan@tootallnate.net>"
@@ -34,7 +34,7 @@
     "node-gyp-build": "^4.2.1",
     "mocha": "^7.1.1",
     "nyc": "^15.0.0",
-    "@napi-ffi/ref-napi": "^3.0.5",
+    "@napi-ffi/ref-napi": "^3.0.7",
     "@napi-ffi/ref-struct-di": "^1.1.1"
   }
 }
diff --git a/test/union.js b/test/union.js
index c664c65..0224c42 100644
--- a/test/union.js
+++ b/test/union.js
@@ -51,9 +51,9 @@ describe('Union', function () {
         , 'sval': 'string'
       })
 
-      assert.strictEqual(ref.types.int, U.fields.ival.type)
-      assert.strictEqual(ref.types.long, U.fields.lval.type)
-      assert.strictEqual(ref.coerceType('string'), U.fields.sval.type)
+      assert.strictEqual(ref.types.int, U.allFields.ival.type)
+      assert.strictEqual(ref.types.long, U.allFields.lval.type)
+      assert.strictEqual(ref.coerceType('string'), U.allFields.sval.type)
     })
 
   })
@@ -86,7 +86,7 @@ describe('Union', function () {
           assert.equal(expectedAlignment, unionType.alignment, 'test' + testNumber +
             ': __alignof__(): expected ' + unionType.alignment + ' to equal ' + expectedAlignment)
         })
-        Object.keys(unionType.fields).forEach(function (name) {
+        Object.keys(unionType.allFields).forEach(function (name) {
           if ('skip' == name) return;
           // these tests just verify the assumption that the
           // offset of every field is always 0