diff --git a/src/cmd/go/internal/modcmd/download.go b/src/cmd/go/internal/modcmd/download.go
index b1f26975bc..373accef06 100644
--- a/src/cmd/go/internal/modcmd/download.go
+++ b/src/cmd/go/internal/modcmd/download.go
@@ -155,7 +155,10 @@ func runDownload(ctx context.Context, cmd *base.Command, args []string) {
 				// 'go mod graph', and similar commands.
 				_, err := modload.LoadModGraph(ctx, "")
 				if err != nil {
-					base.Fatal(err)
+					// TODO(#64008): call base.Fatalf instead of toolchain.SwitchOrFatal
+					// here, since we can only reach this point with an outdated toolchain
+					// if the go.mod file is inconsistent.
+					toolchain.SwitchOrFatal(ctx, err)
 				}
 
 				for _, m := range modFile.Require {
@@ -207,6 +210,16 @@ func runDownload(ctx context.Context, cmd *base.Command, args []string) {
 	// no explicit arguments (their go.mod file should already list an appropriate
 	// toolchain version) or only one module (as is used by the Go Module Proxy).
 
+	if infosErr != nil {
+		var sw toolchain.Switcher
+		sw.Error(infosErr)
+		if sw.NeedSwitch() {
+			sw.Switch(ctx)
+		}
+		// Otherwise, wait to report infosErr after we have downloaded
+		// when we can.
+	}
+
 	if !haveExplicitArgs && modload.WorkFilePath() == "" {
 		// 'go mod download' is sometimes run without arguments to pre-populate the
 		// module cache. In modules that aren't at go 1.17 or higher, it may fetch
@@ -215,20 +228,12 @@ func runDownload(ctx context.Context, cmd *base.Command, args []string) {
 		// (golang.org/issue/45332). We do still fix inconsistencies in go.mod
 		// though.
 		//
-		// TODO(#45551): In the future, report an error if go.mod or go.sum need to
+		// TODO(#64008): In the future, report an error if go.mod or go.sum need to
 		// be updated after loading the build list. This may require setting
 		// the mode to "mod" or "readonly" depending on haveExplicitArgs.
 		if err := modload.WriteGoMod(ctx, modload.WriteOpts{}); err != nil {
 			base.Fatal(err)
 		}
-	} else if infosErr != nil {
-		var sw toolchain.Switcher
-		sw.Error(infosErr)
-		if sw.NeedSwitch() {
-			sw.Switch(ctx)
-		}
-		// Otherwise, wait to report infosErr after we have downloaded
-		// when we can.
 	}
 
 	var downloadErrs sync.Map
diff --git a/src/cmd/go/testdata/script/gotoolchain_modcmds.txt b/src/cmd/go/testdata/script/gotoolchain_modcmds.txt
index 64db6d9666..1edd6d85a5 100644
--- a/src/cmd/go/testdata/script/gotoolchain_modcmds.txt
+++ b/src/cmd/go/testdata/script/gotoolchain_modcmds.txt
@@ -3,19 +3,18 @@ env TESTGO_VERSION_SWITCH=switch
 
 # If the main module's go.mod file lists a version lower than the version
 # required by its dependencies, the commands that fetch and diagnose the module
-# graph (such as 'go mod download' and 'go mod graph') should fail explicitly:
+# graph (such as 'go mod graph' and 'go mod verify') should fail explicitly:
 # they can't interpret the graph themselves, and they aren't allowed to update
 # the go.mod file to record a specific, stable toolchain version that can.
 
-! go mod download
-stderr '^go: rsc.io/future@v1.0.0: module rsc.io/future@v1.0.0 requires go >= 1.999 \(running go 1.21.0\)'
-
 ! go mod verify
 stderr '^go: rsc.io/future@v1.0.0: module rsc.io/future@v1.0.0 requires go >= 1.999 \(running go 1.21.0\)'
 
 ! go mod graph
 stderr '^go: rsc.io/future@v1.0.0: module rsc.io/future@v1.0.0 requires go >= 1.999 \(running go 1.21.0\)'
 
+# TODO(#64008): 'go mod download' without arguments should fail too.
+
 
 # 'go get' should update the main module's go.mod file to a version compatible with the
 # go version required for rsc.io/future, not fail.
diff --git a/src/cmd/go/testdata/script/mod_download_exec_toolchain.txt b/src/cmd/go/testdata/script/mod_download_exec_toolchain.txt
index e441457754..6cf863b28a 100644
--- a/src/cmd/go/testdata/script/mod_download_exec_toolchain.txt
+++ b/src/cmd/go/testdata/script/mod_download_exec_toolchain.txt
@@ -87,10 +87,9 @@ cmp go.mod go.mod.121
 # If an upgrade is needed, GOTOOLCHAIN=auto should perform
 # the upgrade and record the resulting toolchain version.
 
-env GOTOOLCHAIN=go1.21
-! go mod download
-stderr 'rsc.io/needall@v0.0.1 requires go >= 1.23'
-! stderr switching
+env GOTOOLCHAIN=auto
+go mod download
+stderr '^go: module rsc.io/needall@v0.0.1 requires go >= 1.23; switching to go1.23.9$'
 cmp go.mod go.mod.final
 
 
@@ -101,6 +100,8 @@ go 1.21
 -- example/go.mod.final --
 module example
 
-go 1.21
+go 1.23
+
+toolchain go1.23.9
 
 require rsc.io/needall v0.0.1