diff --git a/lib/utility.d.ts b/lib/utility.d.ts
index d6c9c8f..c7df1e7 100644
--- a/lib/utility.d.ts
+++ b/lib/utility.d.ts
@@ -7,6 +7,12 @@ export declare class Utility {
      * @param setting The setting that needs to be supplied as the value for that key.
      */
     resolveSettings(key: string, setting: string | CharacterSets | BackgroundSets | undefined): string;
+    /**
+     * Validates dimensions and returns dimension is correct format.
+     * @param width Width of the image
+     * @param height Height of the image
+     */
+    containsOnlyNumbers(width: number, height: number): boolean;
     /**
      * Validates dimensions and returns dimension is correct format.
      * @param width Width of the image
diff --git a/lib/utility.js b/lib/utility.js
index f292a64..afe7dd7 100644
--- a/lib/utility.js
+++ b/lib/utility.js
@@ -15,6 +15,15 @@ class Utility {
         }
         return `${key}=${setting}&`;
     }
+    /**
+     * Validates dimensions and returns dimension is correct format.
+     * @param width Width of the image
+     * @param height Height of the image
+     */
+    containsOnlyNumbers(width, height) {
+        const onlyNumbersRegEx = /^\d+$/;
+        return onlyNumbersRegEx.test(width.toString()) && onlyNumbersRegEx.test(height.toString());
+    }
     /**
      * Validates dimensions and returns dimension is correct format.
      * @param width Width of the image
@@ -24,6 +33,9 @@ class Utility {
         if (!width || !height) {
             return "";
         }
+        if (!this.containsOnlyNumbers(width, height)) {
+            return "";
+        }
         return `${width}x${height}`;
     }
     /**
diff --git a/src/utility.ts b/src/utility.ts
index b5b8471..a2b5bb5 100644
--- a/src/utility.ts
+++ b/src/utility.ts
@@ -18,6 +18,16 @@ export class Utility {
         return `${key}=${setting}&`;
     }
 
+    /**
+     * Validates dimensions and returns dimension is correct format.
+     * @param width Width of the image
+     * @param height Height of the image
+     */
+    public containsOnlyNumbers(width: number, height: number): boolean {
+        const onlyNumbersRegEx = /^\d+$/;
+        return onlyNumbersRegEx.test(width.toString()) && onlyNumbersRegEx.test(height.toString());
+    }
+
     /**
      * Validates dimensions and returns dimension is correct format.
      * @param width Width of the image
@@ -27,6 +37,11 @@ export class Utility {
         if (!width || !height) {
             return "";
         }
+
+        if (!this.containsOnlyNumbers(width, height)) {
+            return "";
+        }
+
         return `${width}x${height}`;
     }
 
diff --git a/tests/robohash-avatars.test.js b/tests/robohash-avatars.test.js
index 8942296..9d5d62f 100644
--- a/tests/robohash-avatars.test.js
+++ b/tests/robohash-avatars.test.js
@@ -67,7 +67,7 @@ describe("generateAvatar()", function () {
         assert.equal(actual, "https://robohash.org/tonystark?set=set4&bgset=bg1&size=400x400");
     }); 
 
-    it("allz inputs supplied", function () {
+    it("valid username but other undefined inputs supplied", function () {
         console.log("\t", "[test]", this.test.title);
         var actual = avatars.generateAvatar({
             username: "tonystark",
@@ -78,5 +78,64 @@ describe("generateAvatar()", function () {
         }); 
         assert.equal(actual, "https://robohash.org/tonystark");
     }); 
+
+    it("all undefined inputs supplied", function () {
+        console.log("\t", "[test]", this.test.title);
+        var actual = avatars.generateAvatar({
+            username: undefined,
+            background: undefined,
+            characters: undefined,
+            height: undefined,
+            width: undefined
+        }); 
+        assert.equal(actual, "https://robohash.org/RobohashAvatarNPM");
+    }); 
+
+    it("username and character set supplied", function () {
+        console.log("\t", "[test]", this.test.title);
+        var actual = avatars.generateAvatar({
+            username: "peterparker",
+            characters: avatars.CharacterSets.Monsters,
+        }); 
+        assert.equal(actual, "https://robohash.org/peterparker?set=set2");
+    }); 
+
+    it("width but no height supplied", function () {
+        console.log("\t", "[test]", this.test.title);
+        var actual = avatars.generateAvatar({
+            username: "peterparker", 
+            width: 400
+        }); 
+        assert.equal(actual, "https://robohash.org/peterparker");
+    }); 
+
+    it("height but no width supplied", function () {
+        console.log("\t", "[test]", this.test.title);
+        var actual = avatars.generateAvatar({
+            username: "peterparker", 
+            height: 400
+        }); 
+        assert.equal(actual, "https://robohash.org/peterparker");
+    }); 
+
+    it("height and width supplied as string", function () {
+        console.log("\t", "[test]", this.test.title);
+        var actual = avatars.generateAvatar({
+            username: "peterparker", 
+            height: "400",
+            width: "600"
+        }); 
+        assert.equal(actual, "https://robohash.org/peterparker?size=600x400");
+    }); 
+
+    it("height and width supplied as string alphabets", function () {
+        console.log("\t", "[test]", this.test.title);
+        var actual = avatars.generateAvatar({
+            username: "peterparker", 
+            height: "abc",
+            width: "ghi"
+        }); 
+        assert.equal(actual, "https://robohash.org/peterparker");
+    }); 
     
 });
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