diff --git a/src/cmd/go/internal/modcmd/download.go b/src/cmd/go/internal/modcmd/download.go
index 9f8c410b82..71b660d6fd 100644
--- a/src/cmd/go/internal/modcmd/download.go
+++ b/src/cmd/go/internal/modcmd/download.go
@@ -5,6 +5,7 @@
 package modcmd
 
 import (
+	"cmd/go/internal/cfg"
 	"encoding/json"
 	"os"
 
@@ -67,6 +68,13 @@ type moduleJSON struct {
 }
 
 func runDownload(cmd *base.Command, args []string) {
+	// Check whether modules are enabled and whether we're in a module.
+	if cfg.Getenv("GO111MODULE") == "off" {
+		base.Fatalf("go: modules disabled by GO111MODULE=off; see 'go help modules'")
+	}
+	if !modload.HasModRoot() && len(args) == 0 {
+		base.Fatalf("go mod download: no modules specified (see 'go help mod download')")
+	}
 	if len(args) == 0 {
 		args = []string{"all"}
 	}
diff --git a/src/cmd/go/testdata/script/mod_off.txt b/src/cmd/go/testdata/script/mod_off.txt
index bc0a7861f4..cada6deb1d 100644
--- a/src/cmd/go/testdata/script/mod_off.txt
+++ b/src/cmd/go/testdata/script/mod_off.txt
@@ -9,6 +9,8 @@ stderr 'go mod init: modules disabled by GO111MODULE=off; see ''go help modules'
 stderr 'go: modules disabled by GO111MODULE=off; see ''go help modules'''
 ! go mod verify
 stderr 'go: modules disabled by GO111MODULE=off; see ''go help modules'''
+! go mod download
+stderr 'go: modules disabled by GO111MODULE=off; see ''go help modules'''
 
 # Same result in an empty directory
 mkdir z
@@ -19,6 +21,8 @@ stderr 'go mod init: modules disabled by GO111MODULE=off; see ''go help modules'
 stderr 'go: modules disabled by GO111MODULE=off; see ''go help modules'''
 ! go mod verify
 stderr 'go: modules disabled by GO111MODULE=off; see ''go help modules'''
+! go mod download
+stderr 'go: modules disabled by GO111MODULE=off; see ''go help modules'''
 
 -- sample.go --
 package sample