diff --git a/internal/pkg/entrypoint/entrypoint.go b/internal/pkg/entrypoint/entrypoint.go
index 2655b610f..f48a8f10b 100644
--- a/internal/pkg/entrypoint/entrypoint.go
+++ b/internal/pkg/entrypoint/entrypoint.go
@@ -53,7 +53,7 @@ func Main() MainReturn {
 
 	options, recordTransformers, err := climain.ParseCommandLine(os.Args)
 	if err != nil {
-		fmt.Fprintln(os.Stderr, os.Args[0], ": ", err)
+		fmt.Fprintln(os.Stderr, "mlr:", err)
 		os.Exit(1)
 	}
 
diff --git a/internal/pkg/lib/time.go b/internal/pkg/lib/time.go
index 815c3bf9b..94c31c327 100644
--- a/internal/pkg/lib/time.go
+++ b/internal/pkg/lib/time.go
@@ -16,9 +16,10 @@ import (
 // platform this is necessary for *changing* TZ mid-process: e.g.  if a DSL
 // statement does 'ENV["TZ"] = Asia/Istanbul'.
 func SetTZFromEnv() error {
-	location, err := time.LoadLocation(os.Getenv("TZ"))
+	tzenv := os.Getenv("TZ")
+	location, err := time.LoadLocation(tzenv)
 	if err != nil {
-		return err
+		return fmt.Errorf("TZ environment variable appears malformed: \"%s\"", tzenv)
 	}
 	time.Local = location
 	return nil
diff --git a/test/cases/dsl-local-date-time-functions/not-a-valid-timezone-2/cmd b/test/cases/dsl-local-date-time-functions/not-a-valid-timezone-2/cmd
new file mode 100644
index 000000000..e7564a54a
--- /dev/null
+++ b/test/cases/dsl-local-date-time-functions/not-a-valid-timezone-2/cmd
@@ -0,0 +1 @@
+mlr --tz .../... -n put -f test/input/sec2localtime-tz.mlr
diff --git a/test/cases/dsl-local-date-time-functions/not-a-valid-timezone-2/experr b/test/cases/dsl-local-date-time-functions/not-a-valid-timezone-2/experr
new file mode 100644
index 000000000..53e67a008
--- /dev/null
+++ b/test/cases/dsl-local-date-time-functions/not-a-valid-timezone-2/experr
@@ -0,0 +1 @@
+mlr: TZ environment variable appears malformed: ".../..."
diff --git a/test/cases/dsl-local-date-time-functions/not-a-valid-timezone-2/expout b/test/cases/dsl-local-date-time-functions/not-a-valid-timezone-2/expout
new file mode 100644
index 000000000..e69de29bb
diff --git a/test/cases/dsl-local-date-time-functions/not-a-valid-timezone-2/should-fail b/test/cases/dsl-local-date-time-functions/not-a-valid-timezone-2/should-fail
new file mode 100644
index 000000000..e69de29bb
diff --git a/test/cases/dsl-local-date-time-functions/not-a-valid-timezone/experr b/test/cases/dsl-local-date-time-functions/not-a-valid-timezone/experr
index fc9d9179d..62865a004 100644
--- a/test/cases/dsl-local-date-time-functions/not-a-valid-timezone/experr
+++ b/test/cases/dsl-local-date-time-functions/not-a-valid-timezone/experr
@@ -1 +1 @@
-${MLR} :  unknown time zone this-is-not-a-valid-timezone-name
+mlr: TZ environment variable appears malformed: "this-is-not-a-valid-timezone-name"