diff --git a/package.json b/package.json
index 1ac8acf..2c543b7 100644
--- a/package.json
+++ b/package.json
@@ -1,6 +1,6 @@
 {
   "name": "ajv-cli",
-  "version": "5.0.0",
+  "version": "5.0.1",
   "description": "Command line interface for Ajv JSON schema validator",
   "scripts": {
     "build": "rimraf dist && tsc",
diff --git a/src/commands/ajv.ts b/src/commands/ajv.ts
index d06acb5..6fa0b74 100644
--- a/src/commands/ajv.ts
+++ b/src/commands/ajv.ts
@@ -85,13 +85,11 @@ export default function (argv: ParsedArgs): AjvCore {
     try {
       registerer = require("ts-node").register()
     } catch (err) {
-      /* istanbul ignore next */
-      if (err.code === "MODULE_NOT_FOUND") {
+      if (err instanceof Error && "code" in err && err.code === "MODULE_NOT_FOUND") {
         throw new Error(
           `'ts-node' is required for the TypeScript configuration files. Make sure it is installed\nError: ${err.message}`
         )
       }
-
       throw err
     }
 
diff --git a/src/commands/util.ts b/src/commands/util.ts
index 42b4ed1..abf31f8 100644
--- a/src/commands/util.ts
+++ b/src/commands/util.ts
@@ -29,6 +29,7 @@ function getFormatFromFileName(filename: string): string {
 function decodeFile(contents: string, format: string): any {
   switch (format) {
     case "json":
+    case "":
       return JSON.parse(contents)
     case "jsonc":
     case "json5":
@@ -52,13 +53,16 @@ export function openFile(filename: string, suffix: string): any {
       json = require(file)
     }
   } catch (err) {
-    const msg: string = err.message
-    console.error(`error:  ${msg.replace(" module", " " + suffix)}`)
+    if (err instanceof Error) {
+      const msg: string = err.message
+      console.error(`error:  ${msg.replace(" module", " " + suffix)}`)
+    }
     process.exit(2)
   }
   return json
 }
 
+// eslint-disable-next-line @typescript-eslint/explicit-module-boundary-types
 export function logJSON(mode: string, data: any, ajv?: Ajv): string {
   switch (mode) {
     case "json":
@@ -81,8 +85,10 @@ export function compile(ajv: Ajv, schemaFile: string): AnyValidateFunction {
   try {
     return ajv.compile(schema)
   } catch (err) {
-    console.error(`schema ${schemaFile} is invalid`)
-    console.error(`error: ${err.message}`)
+    if (err instanceof Error) {
+      console.error(`schema ${schemaFile} is invalid`)
+      console.error(`error: ${err.message}`)
+    }
     process.exit(1)
   }
 }
diff --git a/test/schema_no_ext b/test/schema_no_ext
new file mode 100644
index 0000000..711fed8
--- /dev/null
+++ b/test/schema_no_ext
@@ -0,0 +1,60 @@
+{
+  "$schema": "http://json-schema.org/draft-07/schema#",
+  "$id": "schema.json",
+  "description": "basic schema from z-schema benchmark (https://github.com/zaggino/z-schema)",
+  "title": "Product set",
+  "type": "array",
+  "items": {
+    "title": "Product",
+    "type": "object",
+    "additionalProperties": false,
+    "properties": {
+      "id": {
+        "description": "The unique identifier for a product",
+        "type": "number"
+      },
+      "name": {
+        "type": "string"
+      },
+      "price": {
+        "type": "number",
+        "exclusiveMinimum": 0
+      },
+      "tags": {
+        "type": "array",
+        "items": {
+          "type": "string"
+        },
+        "minItems": 1,
+        "uniqueItems": true
+      },
+      "dimensions": {
+        "type": "object",
+        "properties": {
+          "length": {
+            "type": "number"
+          },
+          "width": {
+            "type": "number"
+          },
+          "height": {
+            "type": "number"
+          }
+        },
+        "required": [
+          "length",
+          "width",
+          "height"
+        ]
+      },
+      "warehouseLocation": {
+        "description": "Coordinates of the warehouse with the product"
+      }
+    },
+    "required": [
+      "id",
+      "name",
+      "price"
+    ]
+  }
+}
diff --git a/test/valid_data_no_ext b/test/valid_data_no_ext
new file mode 100644
index 0000000..90fe498
--- /dev/null
+++ b/test/valid_data_no_ext
@@ -0,0 +1,34 @@
+[
+  {
+    "id": 2,
+    "name": "An ice sculpture",
+    "price": 12.5,
+    "tags": [
+      "cold",
+      "ice"
+    ],
+    "dimensions": {
+      "length": 7,
+      "width": 12,
+      "height": 9.5
+    },
+    "warehouseLocation": {
+      "latitude": -78.75,
+      "longitude": 20.4
+    }
+  },
+  {
+    "id": 3,
+    "name": "A blue mouse",
+    "price": 25.5,
+    "dimensions": {
+      "length": 3.1,
+      "width": 1,
+      "height": 1
+    },
+    "warehouseLocation": {
+      "latitude": 54.4,
+      "longitude": -32.7
+    }
+  }
+]
diff --git a/test/validate.spec.ts b/test/validate.spec.ts
index 109f91e..4d71a40 100644
--- a/test/validate.spec.ts
+++ b/test/validate.spec.ts
@@ -42,8 +42,24 @@ describe("validate", function () {
       })
     })
 
-    it('should validate valid data with the "jsonc" extension', (done) => {
-      cli("-s test/schema -d test/valid_data.jsonc", (error, stdout, stderr) => {
+    it("should try JSON format if data file has no extension", (done) => {
+      cli("-s test/schema -d test/valid_data_no_ext", (error, stdout, stderr) => {
+        assert.strictEqual(error, null)
+        assertValid(stdout, 1)
+        assert.strictEqual(stderr, "")
+        done()
+      })
+    })
+    it("should try JSON format if schema file has no extension", (done) => {
+      cli("-s test/schema_no_ext -d test/valid_data.json", (error, stdout, stderr) => {
+        assert.strictEqual(error, null)
+        assertValid(stdout, 1)
+        assert.strictEqual(stderr, "")
+        done()
+      })
+    })
+    it("should try JSON format if schema and data file have no extension", (done) => {
+      cli("-s test/schema_no_ext -d test/valid_data_no_ext", (error, stdout, stderr) => {
         assert.strictEqual(error, null)
         assertValid(stdout, 1)
         assert.strictEqual(stderr, "")
@@ -63,6 +79,7 @@ describe("validate", function () {
       )
     })
 
+
     it("should validate invalid data", (done) => {
       cli(
         "-s test/schema.json -d test/invalid_data.json --errors=line",