diff --git a/CHANGELOG.md b/CHANGELOG.md
index 1d1d829c..63c45737 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -11,6 +11,7 @@
 - Rendered more hooks than during the previous render in `FileList`
 - [#142](https://github.com/estruyf/vscode-front-matter/issues/142): Fix for unknown tags where it throws an error
 - [#143](https://github.com/estruyf/vscode-front-matter/issues/143): Fix for duplicate values in the file list
+- [#144](https://github.com/estruyf/vscode-front-matter/issues/144): Fix for `toISOString` does not exist on object
 
 ## [5.0.0] - 2021-10-07 - [Release Notes](https://beta.frontmatter.codes/updates/v5.0.0)
 
diff --git a/src/commands/Article.ts b/src/commands/Article.ts
index b6a3f44f..f7a3633c 100644
--- a/src/commands/Article.ts
+++ b/src/commands/Article.ts
@@ -245,7 +245,7 @@ export class Article {
     if (dateFormat && typeof dateFormat === "string") {
       return format(dateValue, dateFormat);
     } else {
-      return dateValue.toISOString();
+      return typeof dateValue.toISOString === 'function' ? dateValue.toISOString() : dateValue;
     }
   }
 
diff --git a/src/panelWebView/components/Fields/DateTimeField.tsx b/src/panelWebView/components/Fields/DateTimeField.tsx
index b18b0c65..2354b4f7 100644
--- a/src/panelWebView/components/Fields/DateTimeField.tsx
+++ b/src/panelWebView/components/Fields/DateTimeField.tsx
@@ -30,7 +30,10 @@ export const DateTimeField: React.FunctionComponent<IDateTimeFieldProps> = ({lab
   };
 
   React.useEffect(() => {
-    if (dateValue?.toISOString() !== date?.toISOString()) {
+    const crntValue = typeof date?.toISOString === 'function' ? date.toISOString() : date;
+    const stateValue = typeof dateValue?.toISOString === 'function' ? dateValue.toISOString() : dateValue;
+
+    if (crntValue !== stateValue) {
       setDateValue(date);
     }
   }, [ date ]);
@@ -45,7 +48,7 @@ export const DateTimeField: React.FunctionComponent<IDateTimeFieldProps> = ({lab
       
       <div className={`metadata_field__datetime`}>
         <DatePicker
-          selected={dateValue as Date}
+          selected={dateValue as Date || null}
           onChange={onDateChange}
           timeInputLabel="Time:"
           dateFormat={format || "MM/dd/yyyy HH:mm"}