diff --git a/components/engine/api/swagger.yaml b/components/engine/api/swagger.yaml
index 746d815356..41016f18cd 100644
--- a/components/engine/api/swagger.yaml
+++ b/components/engine/api/swagger.yaml
@@ -754,7 +754,7 @@ definitions:
         default: false
       Env:
         description: |
-          A list of environment variables to set inside the container in the form `["VAR=value", ...]`
+          A list of environment variables to set inside the container in the form `["VAR=value", ...]`. A variable without `=` is removed from the environment, rather than to have an empty value.
         type: "array"
         items:
           type: "string"
diff --git a/components/engine/container/env_test.go b/components/engine/container/env_test.go
index fb304fe361..4ebf2640a8 100644
--- a/components/engine/container/env_test.go
+++ b/components/engine/container/env_test.go
@@ -4,11 +4,14 @@ import "testing"
 
 func TestReplaceAndAppendEnvVars(t *testing.T) {
 	var (
-		d = []string{"HOME=/"}
-		o = []string{"HOME=/root", "TERM=xterm"}
+		d = []string{"HOME=/", "FOO=foo_default"}
+		// remove FOO from env
+		// remove BAR from env (nop)
+		o = []string{"HOME=/root", "TERM=xterm", "FOO", "BAR"}
 	)
 
 	env := ReplaceOrAppendEnvValues(d, o)
+	t.Logf("default=%v, override=%v, result=%v", d, o, env)
 	if len(env) != 2 {
 		t.Fatalf("expected len of 2 got %d", len(env))
 	}