diff --git a/src/cmd/go/internal/modload/init.go b/src/cmd/go/internal/modload/init.go
index 777b63841f..120afef4ff 100644
--- a/src/cmd/go/internal/modload/init.go
+++ b/src/cmd/go/internal/modload/init.go
@@ -354,7 +354,7 @@ func (goModDirtyError) Error() string {
 		return fmt.Sprintf("updates to go.mod needed, disabled by -mod=%v; to update it:\n\tgo mod tidy", cfg.BuildMod)
 	}
 	if cfg.BuildModReason != "" {
-		return fmt.Sprintf("updates to go.mod needed, disabled by -mod=%s\n\t(%s)\n\tto update it:\n\t", cfg.BuildMod, cfg.BuildModReason)
+		return fmt.Sprintf("updates to go.mod needed, disabled by -mod=%s\n\t(%s)\n\tto update it:\n\tgo mod tidy", cfg.BuildMod, cfg.BuildModReason)
 	}
 	return "updates to go.mod needed; to update it:\n\tgo mod tidy"
 }
diff --git a/src/cmd/go/testdata/script/mod_require_exclude.txt b/src/cmd/go/testdata/script/mod_require_exclude.txt
index 5b6143da42..0946dbf0bb 100644
--- a/src/cmd/go/testdata/script/mod_require_exclude.txt
+++ b/src/cmd/go/testdata/script/mod_require_exclude.txt
@@ -17,6 +17,17 @@ stderr '^go: updates to go.mod needed, disabled by -mod=vendor; to update it:\n\
 ! stdout '^rsc.io/sampler v1.99.99'
 cmp go.mod go.mod.orig
 
+# The failure message should be clear when -mod=vendor is implicit.
+
+go mod edit -go=1.14
+! go list -m rsc.io/sampler
+stderr '^go: ignoring requirement on excluded version rsc.io/sampler v1\.99\.99$'
+stderr '^go: updates to go.mod needed, disabled by -mod=vendor\n\t\(Go version in go.mod is at least 1.14 and vendor directory exists\.\)\n\tto update it:\n\tgo mod tidy$'
+! stdout '^rsc.io/sampler v1.99.99'
+go mod edit -go=1.13
+cmp go.mod go.mod.orig
+
+
 # With the selected version excluded, commands that load only modules should
 # drop the excluded module.
 
@@ -58,7 +69,11 @@ module x
 go 1.13
 
 exclude rsc.io/sampler v1.99.99
+
 require rsc.io/sampler v1.99.99
+-- vendor/modules.txt --
+# rsc.io/sampler v1.99.99
+## explicit
 -- go.moddrop --
 module x