diff --git a/bin/cli.js b/bin/cli.js
index c045a2c..966621d 100755
--- a/bin/cli.js
+++ b/bin/cli.js
@@ -123,7 +123,7 @@ if (opt.load) {
 
 function fileIO(result) {
     for (let a of result.atlas) {
-        const imageName = a.id ? `${a.name}.${a.id}.${a.ext}` : `${a.name}.${a.ext}`
+        const imageName = a.hasOwnProperty("id") ? `${a.name}.${a.id}.${a.ext}` : `${a.name}.${a.ext}`
         a.image.writeAsync(imageName)
         .then(() => {
             console.log(`Saved atlas: ${imageName}`);
@@ -133,7 +133,7 @@ function fileIO(result) {
         });
     }
     for (let s of result.spritesheets) {
-        const sheetName = s.id ? `${s.name}.${s.id}.${s.ext}` : `${s.name}.${s.ext}`;
+        const sheetName = s.hasOwnProperty("id") ? `${s.name}.${s.id}.${s.ext}` : `${s.name}.${s.ext}`;
         fs.writeFile(sheetName, result.exporter.compile(s), 'utf-8', err => {
             if(err) console.error(`Failed saving spritesheet ${sheetName}: ${err}`);
             else console.log(`Saved spritesheet: ${sheetName}`);
diff --git a/src/atlasify.ts b/src/atlasify.ts
index 98ba35d..be46fc7 100644
--- a/src/atlasify.ts
+++ b/src/atlasify.ts
@@ -284,7 +284,7 @@ export class Atlasify {
         this._packer.bins.forEach((bin, index: number) => {
             // Count tags
             let tag = bin.tag ? bin.tag : "_";
-            if (!tagCount[tag]) tagCount[tag] = 0; // create index key if not exist
+            if (!tagCount.hasOwnProperty(tag)) tagCount[tag] = 0; // create index key if not exist
             else tagCount[tag]++;
 
             if (!bin.dirty) return; // early return if bin is not changed
@@ -561,11 +561,11 @@ export class Atlasify {
     private pruneTagIndex (tagCount: { [index: string]: number; }) {
         for (let a of this._atlas) {
             const tag = a.tag ? a.tag : "_";
-            if (tagCount[tag] < 2 && a.id) delete a.id;
+            if (tagCount[tag] < 1 && a.id) delete a.id;
         }
         for (let s of this._spritesheets) {
             const tag = s.tag ? s.tag : "_";
-            if (tagCount[tag] < 2 && s.id) delete s.id;
+            if (tagCount[tag] < 1 && s.id) delete s.id;
         }
     }
 }