diff --git a/lib/command.js b/lib/command.js
index 590a271dd..4a9867cb1 100644
--- a/lib/command.js
+++ b/lib/command.js
@@ -780,7 +780,7 @@ Expecting one of '${allowedValues.join("', '")}'`);
    */
 
   setOptionValue(key, value) {
-    return this.setOptionValueWithSource(key, value, undefined);
+    return this.setOptionValueWithSource(key, value);
   }
 
   /**
@@ -788,7 +788,7 @@ Expecting one of '${allowedValues.join("', '")}'`);
     *
     * @param {string} key
     * @param {Object} value
-    * @param {string} source - expected values are default/config/env/cli/implied
+    * @param {string} [source] - expected values are default/config/env/cli/implied
     * @return {Command} `this` command for chaining
     */
 
@@ -807,7 +807,7 @@ Expecting one of '${allowedValues.join("', '")}'`);
     * Expected values are default | config | env | cli | implied
     *
     * @param {string} key
-    * @return {string}
+    * @return {string | undefined}
     */
 
   getOptionValueSource(key) {
@@ -819,7 +819,7 @@ Expecting one of '${allowedValues.join("', '")}'`);
     * Expected values are default | config | env | cli | implied
     *
     * @param {string} key
-    * @return {string}
+    * @return {string | undefined}
     */
 
   getOptionValueSourceWithGlobals(key) {
diff --git a/typings/index.d.ts b/typings/index.d.ts
index 695c3bd25..8fa682e20 100644
--- a/typings/index.d.ts
+++ b/typings/index.d.ts
@@ -595,17 +595,17 @@ export class Command {
   /**
    * Store option value and where the value came from.
    */
-  setOptionValueWithSource(key: string, value: unknown, source: OptionValueSource): this;
+  setOptionValueWithSource(key: string, value: unknown, source?: OptionValueSource | string | undefined): this;
 
   /**
    * Get source of option value.
    */
-  getOptionValueSource(key: string): OptionValueSource | undefined;
+  getOptionValueSource(key: string): OptionValueSource | string | undefined;
 
   /**
     * Get source of option value. See also .optsWithGlobals().
    */
-  getOptionValueSourceWithGlobals(key: string): OptionValueSource | undefined;
+  getOptionValueSourceWithGlobals(key: string): OptionValueSource | string | undefined;
 
   /**
    * Alter parsing of short flags with optional values.
diff --git a/typings/index.test-d.ts b/typings/index.test-d.ts
index 734036fad..5d83446da 100644
--- a/typings/index.test-d.ts
+++ b/typings/index.test-d.ts
@@ -173,10 +173,10 @@ expectType<commander.Command>(program.setOptionValue('example', true));
 expectType<commander.Command>(program.setOptionValueWithSource('example', [], 'cli'));
 
 // getOptionValueSource
-expectType<commander.OptionValueSource | undefined>(program.getOptionValueSource('example'));
+expectType<string | undefined>(program.getOptionValueSource('example'));
 
 // getOptionValueSourceWithGlobals
-expectType<commander.OptionValueSource | undefined>(program.getOptionValueSourceWithGlobals('example'));
+expectType<string | undefined>(program.getOptionValueSourceWithGlobals('example'));
 
 // combineFlagAndOptionalValue
 expectType<commander.Command>(program.combineFlagAndOptionalValue());