diff --git a/CHANGELOG.md b/CHANGELOG.md
index 81c36aa1..a71ae25c 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -1,5 +1,10 @@
 # Changelog
 
+## Unreleased
+
+- Small optimization and bug fix: don't compute variables if not needed for
+  `dotenv:` ([#517](https://github.com/go-task/task/issues/517)).
+
 ## v3.5.0 - 2021-07-04
 
 - Add support for interpolation in `dotenv:`
diff --git a/taskfile/read/dotenv.go b/taskfile/read/dotenv.go
index 8d8ffd00..0ce6fed4 100644
--- a/taskfile/read/dotenv.go
+++ b/taskfile/read/dotenv.go
@@ -12,6 +12,10 @@ import (
 )
 
 func Dotenv(c compiler.Compiler, tf *taskfile.Taskfile, dir string) (*taskfile.Vars, error) {
+	if len(tf.Dotenv) == 0 {
+		return nil, nil
+	}
+
 	vars, err := c.GetTaskfileVariables()
 	if err != nil {
 		return nil, err