diff --git a/README.md b/README.md
index 980f536..ff98095 100644
--- a/README.md
+++ b/README.md
@@ -475,7 +475,8 @@ Object containing environment variables (both getter and setter). Shortcut to pr
 ### exec(command [, options] [, callback])
 Available options (all `false` by default):
 
-+ `async`: Asynchronous execution. Defaults to true if a callback is provided.
++ `async`: Asynchronous execution. If a callback is provided, it will be set to
+  `true`, regardless of the passed value.
 + `silent`: Do not echo program output to console.
 
 Examples:
diff --git a/src/exec.js b/src/exec.js
index 87a6c30..0c5408b 100644
--- a/src/exec.js
+++ b/src/exec.js
@@ -182,7 +182,8 @@ function execAsync(cmd, opts, callback) {
 //@ ### exec(command [, options] [, callback])
 //@ Available options (all `false` by default):
 //@
-//@ + `async`: Asynchronous execution. Defaults to true if a callback is provided.
+//@ + `async`: Asynchronous execution. If a callback is provided, it will be set to
+//@   `true`, regardless of the passed value.
 //@ + `silent`: Do not echo program output to console.
 //@
 //@ Examples: