diff --git a/go/internal/packagesdriver/sizes.go b/go/internal/packagesdriver/sizes.go
index dc6177c..35bc6a4 100644
--- a/go/internal/packagesdriver/sizes.go
+++ b/go/internal/packagesdriver/sizes.go
@@ -39,7 +39,12 @@
 	}
 
 	if tool == "off" {
-		return GetSizesGolist(ctx, buildFlags, env, gocmdRunner, dir)
+		inv := gocommand.Invocation{
+			BuildFlags: buildFlags,
+			Env:        env,
+			WorkingDir: dir,
+		}
+		return GetSizesGolist(ctx, inv, gocmdRunner)
 	}
 
 	req, err := json.Marshal(struct {
@@ -75,26 +80,17 @@
 	return response.Sizes, nil
 }
 
-func GetSizesGolist(ctx context.Context, buildFlags, env []string, gocmdRunner *gocommand.Runner, dir string) (types.Sizes, error) {
-	inv := gocommand.Invocation{
-		Verb:       "list",
-		Args:       []string{"-f", "{{context.GOARCH}} {{context.Compiler}}", "--", "unsafe"},
-		Env:        env,
-		BuildFlags: buildFlags,
-		WorkingDir: dir,
-	}
+func GetSizesGolist(ctx context.Context, inv gocommand.Invocation, gocmdRunner *gocommand.Runner) (types.Sizes, error) {
+	inv.Verb = "list"
+	inv.Args = []string{"-f", "{{context.GOARCH}} {{context.Compiler}}", "--", "unsafe"}
 	stdout, stderr, friendlyErr, rawErr := gocmdRunner.RunRaw(ctx, inv)
 	var goarch, compiler string
 	if rawErr != nil {
 		if strings.Contains(rawErr.Error(), "cannot find main module") {
 			// User's running outside of a module. All bets are off. Get GOARCH and guess compiler is gc.
 			// TODO(matloob): Is this a problem in practice?
-			inv := gocommand.Invocation{
-				Verb:       "env",
-				Args:       []string{"GOARCH"},
-				Env:        env,
-				WorkingDir: dir,
-			}
+			inv.Verb = "env"
+			inv.Args = []string{"GOARCH"}
 			envout, enverr := gocmdRunner.Run(ctx, inv)
 			if enverr != nil {
 				return nil, enverr
diff --git a/go/packages/golist.go b/go/packages/golist.go
index d7dac20..2696cfb 100644
--- a/go/packages/golist.go
+++ b/go/packages/golist.go
@@ -139,6 +139,12 @@
 
 	response := newDeduper()
 
+	state := &golistState{
+		cfg:        cfg,
+		ctx:        ctx,
+		vendorDirs: map[string]bool{},
+	}
+
 	// Fill in response.Sizes asynchronously if necessary.
 	var sizeserr error
 	var sizeswg sync.WaitGroup
@@ -146,19 +152,13 @@
 		sizeswg.Add(1)
 		go func() {
 			var sizes types.Sizes
-			sizes, sizeserr = packagesdriver.GetSizesGolist(ctx, cfg.BuildFlags, cfg.Env, cfg.gocmdRunner, cfg.Dir)
+			sizes, sizeserr = packagesdriver.GetSizesGolist(ctx, state.cfgInvocation(), cfg.gocmdRunner)
 			// types.SizesFor always returns nil or a *types.StdSizes.
 			response.dr.Sizes, _ = sizes.(*types.StdSizes)
 			sizeswg.Done()
 		}()
 	}
 
-	state := &golistState{
-		cfg:        cfg,
-		ctx:        ctx,
-		vendorDirs: map[string]bool{},
-	}
-
 	// Determine files requested in contains patterns
 	var containFiles []string
 	restPatterns := make([]string, 0, len(patterns))
@@ -839,18 +839,26 @@
 	return fullargs
 }
 
-// invokeGo returns the stdout of a go command invocation.
-func (state *golistState) invokeGo(verb string, args ...string) (*bytes.Buffer, error) {
+// cfgInvocation returns an Invocation that reflects cfg's settings.
+func (state *golistState) cfgInvocation() gocommand.Invocation {
 	cfg := state.cfg
-
-	inv := gocommand.Invocation{
-		Verb:       verb,
-		Args:       args,
+	return gocommand.Invocation{
 		BuildFlags: cfg.BuildFlags,
+		ModFile:    cfg.modFile,
+		ModFlag:    cfg.modFlag,
 		Env:        cfg.Env,
 		Logf:       cfg.Logf,
 		WorkingDir: cfg.Dir,
 	}
+}
+
+// invokeGo returns the stdout of a go command invocation.
+func (state *golistState) invokeGo(verb string, args ...string) (*bytes.Buffer, error) {
+	cfg := state.cfg
+
+	inv := state.cfgInvocation()
+	inv.Verb = verb
+	inv.Args = args
 	gocmdRunner := cfg.gocmdRunner
 	if gocmdRunner == nil {
 		gocmdRunner = &gocommand.Runner{}
diff --git a/go/packages/packages.go b/go/packages/packages.go
index 970c480..38475e8 100644
--- a/go/packages/packages.go
+++ b/go/packages/packages.go
@@ -144,6 +144,12 @@
 	// the build system's query tool.
 	BuildFlags []string
 
+	// modFile will be used for -modfile in go command invocations.
+	modFile string
+
+	// modFlag will be used for -modfile in go command invocations.
+	modFlag string
+
 	// Fset provides source position information for syntax trees and types.
 	// If Fset is nil, Load will use a new fileset, but preserve Fset's value.
 	Fset *token.FileSet
@@ -366,6 +372,12 @@
 	packagesinternal.SetGoCmdRunner = func(config interface{}, runner *gocommand.Runner) {
 		config.(*Config).gocmdRunner = runner
 	}
+	packagesinternal.SetModFile = func(config interface{}, value string) {
+		config.(*Config).modFile = value
+	}
+	packagesinternal.SetModFlag = func(config interface{}, value string) {
+		config.(*Config).modFlag = value
+	}
 	packagesinternal.TypecheckCgo = int(typecheckCgo)
 }
 
diff --git a/internal/gocommand/invoke.go b/internal/gocommand/invoke.go
index f516e17..b5c061b 100644
--- a/internal/gocommand/invoke.go
+++ b/internal/gocommand/invoke.go
@@ -130,6 +130,8 @@
 	Verb       string
 	Args       []string
 	BuildFlags []string
+	ModFlag    string
+	ModFile    string
 	Env        []string
 	WorkingDir string
 	Logf       func(format string, args ...interface{})
@@ -158,17 +160,35 @@
 	}
 
 	goArgs := []string{i.Verb}
+
+	appendModFile := func() {
+		if i.ModFile != "" {
+			goArgs = append(goArgs, "-modfile="+i.ModFile)
+		}
+	}
+	appendModFlag := func() {
+		if i.ModFlag != "" {
+			goArgs = append(goArgs, "-mod="+i.ModFlag)
+		}
+	}
+
 	switch i.Verb {
-	case "mod":
-		// mod needs the sub-verb before build flags.
-		goArgs = append(goArgs, i.Args[0])
-		goArgs = append(goArgs, i.BuildFlags...)
-		goArgs = append(goArgs, i.Args[1:]...)
-	case "env":
-		// env doesn't take build flags.
+	case "env", "version":
 		goArgs = append(goArgs, i.Args...)
-	default:
+	case "mod":
+		// mod needs the sub-verb before flags.
+		goArgs = append(goArgs, i.Args[0])
+		appendModFile()
+		goArgs = append(goArgs, i.Args[1:]...)
+	case "get":
 		goArgs = append(goArgs, i.BuildFlags...)
+		appendModFile()
+		goArgs = append(goArgs, i.Args...)
+
+	default: // notably list and build.
+		goArgs = append(goArgs, i.BuildFlags...)
+		appendModFile()
+		appendModFlag()
 		goArgs = append(goArgs, i.Args...)
 	}
 	cmd := exec.Command("go", goArgs...)
diff --git a/internal/imports/fix.go b/internal/imports/fix.go
index 7a8e93f..d859617 100644
--- a/internal/imports/fix.go
+++ b/internal/imports/fix.go
@@ -804,6 +804,8 @@
 	GocmdRunner *gocommand.Runner
 
 	BuildFlags []string
+	ModFlag    string
+	ModFile    string
 
 	// Env overrides the OS environment, and can be used to specify
 	// GOPROXY, GO111MODULE, etc. PATH cannot be set here, because
diff --git a/internal/imports/mod.go b/internal/imports/mod.go
index 6982121..8a83613 100644
--- a/internal/imports/mod.go
+++ b/internal/imports/mod.go
@@ -59,6 +59,8 @@
 	}
 	inv := gocommand.Invocation{
 		BuildFlags: r.env.BuildFlags,
+		ModFlag:    r.env.ModFlag,
+		ModFile:    r.env.ModFile,
 		Env:        r.env.env(),
 		Logf:       r.env.Logf,
 		WorkingDir: r.env.WorkingDir,
diff --git a/internal/lsp/cache/imports.go b/internal/lsp/cache/imports.go
index 6274792..5039eac 100644
--- a/internal/lsp/cache/imports.go
+++ b/internal/lsp/cache/imports.go
@@ -160,9 +160,7 @@
 		return cleanup, err
 	}
 	if modmod {
-		// -mod isn't really a build flag, but we can get away with it given
-		// the set of commands that goimports wants to run.
-		pe.BuildFlags = append([]string{"-mod=mod"}, pe.BuildFlags...)
+		pe.ModFlag = "mod"
 	}
 
 	// Add -modfile to the build flags, if we are using it.
@@ -172,7 +170,7 @@
 		if err != nil {
 			return nil, err
 		}
-		pe.BuildFlags = append(pe.BuildFlags, fmt.Sprintf("-modfile=%s", tmpURI.Filename()))
+		pe.ModFile = tmpURI.Filename()
 	}
 
 	return cleanup, nil
diff --git a/internal/lsp/cache/load.go b/internal/lsp/cache/load.go
index 27cd534..a5ae427 100644
--- a/internal/lsp/cache/load.go
+++ b/internal/lsp/cache/load.go
@@ -92,7 +92,7 @@
 	cleanup := func() {}
 	wdir := s.view.rootURI.Filename()
 
-	var buildFlags []string
+	var modFile string
 	var modURI span.URI
 	var modContent []byte
 	switch {
@@ -141,18 +141,17 @@
 		if err != nil {
 			return err
 		}
-		buildFlags = append(buildFlags, fmt.Sprintf("-modfile=%s", tmpURI.Filename()))
+		modFile = tmpURI.Filename()
 	}
 
 	cfg := s.config(ctx, wdir)
-	cfg.BuildFlags = append(cfg.BuildFlags, buildFlags...)
-
+	packagesinternal.SetModFile(cfg, modFile)
 	modMod, err := s.needsModEqualsMod(ctx, modURI, modContent)
 	if err != nil {
 		return err
 	}
 	if modMod {
-		cfg.BuildFlags = append([]string{"-mod=mod"}, cfg.BuildFlags...)
+		packagesinternal.SetModFlag(cfg, "mod")
 	}
 
 	pkgs, err := packages.Load(cfg, query...)
diff --git a/internal/lsp/cache/mod.go b/internal/lsp/cache/mod.go
index 099b5ce..0c2a96b 100644
--- a/internal/lsp/cache/mod.go
+++ b/internal/lsp/cache/mod.go
@@ -23,6 +23,7 @@
 	"golang.org/x/tools/internal/lsp/protocol"
 	"golang.org/x/tools/internal/lsp/source"
 	"golang.org/x/tools/internal/memoize"
+	"golang.org/x/tools/internal/packagesinternal"
 	"golang.org/x/tools/internal/span"
 	errors "golang.org/x/xerrors"
 )
@@ -329,7 +330,7 @@
 		if s.workspaceMode()&tempModfile == 0 || containsVendor(fh.URI()) {
 			// Use -mod=readonly if the module contains a vendor directory
 			// (see golang/go#38711).
-			args = append([]string{"-mod", "readonly"}, args...)
+			packagesinternal.SetModFlag(cfg, "readonly")
 		}
 		stdout, err := snapshot.runGoCommandWithConfig(ctx, cfg, "list", args)
 		if err != nil {
diff --git a/internal/lsp/cache/snapshot.go b/internal/lsp/cache/snapshot.go
index d141c51..93be75a 100644
--- a/internal/lsp/cache/snapshot.go
+++ b/internal/lsp/cache/snapshot.go
@@ -255,13 +255,14 @@
 func (s *snapshot) goCommandInvocation(ctx context.Context, cfg *packages.Config, allowTempModfile bool, verb string, args []string) (tmpURI span.URI, runner *gocommand.Runner, inv *gocommand.Invocation, cleanup func(), err error) {
 	cleanup = func() {} // fallback
 	modURI := s.GoModForFile(ctx, span.URIFromPath(cfg.Dir))
-	var buildFlags []string
-	// `go mod`, `go env`, and `go version` don't take build flags.
-	switch verb {
-	case "mod", "env", "version":
-	default:
-		buildFlags = append(cfg.BuildFlags, buildFlags...)
+
+	inv = &gocommand.Invocation{
+		Verb:       verb,
+		Args:       args,
+		Env:        cfg.Env,
+		WorkingDir: cfg.Dir,
 	}
+
 	if allowTempModfile && s.workspaceMode()&tempModfile != 0 {
 		if modURI == "" {
 			return "", nil, nil, cleanup, fmt.Errorf("no go.mod file found in %s", cfg.Dir)
@@ -277,40 +278,30 @@
 		if err != nil {
 			return "", nil, nil, cleanup, err
 		}
-		buildFlags = append(buildFlags, fmt.Sprintf("-modfile=%s", tmpURI.Filename()))
+		inv.ModFile = tmpURI.Filename()
 	}
-	// TODO(rstambler): Remove this when golang/go#41826 is resolved.
-	// Don't add -mod=mod for `go mod` or `go get`.
-	switch verb {
-	case "mod", "get":
-	default:
-		var modContent []byte
-		if modURI != "" {
-			modFH, err := s.GetFile(ctx, modURI)
-			if err != nil {
-				return "", nil, nil, cleanup, err
-			}
-			modContent, err = modFH.Read()
-			if err != nil {
-				return "", nil, nil, nil, err
-			}
-		}
-		modMod, err := s.needsModEqualsMod(ctx, modURI, modContent)
+
+	var modContent []byte
+	if modURI != "" {
+		modFH, err := s.GetFile(ctx, modURI)
 		if err != nil {
 			return "", nil, nil, cleanup, err
 		}
-		if modMod {
-			buildFlags = append([]string{"-mod=mod"}, buildFlags...)
+		modContent, err = modFH.Read()
+		if err != nil {
+			return "", nil, nil, nil, err
 		}
 	}
+	modMod, err := s.needsModEqualsMod(ctx, modURI, modContent)
+	if err != nil {
+		return "", nil, nil, cleanup, err
+	}
+	if modMod {
+		inv.ModFlag = "mod"
+	}
+
 	runner = packagesinternal.GetGoCmdRunner(cfg)
-	return tmpURI, runner, &gocommand.Invocation{
-		Verb:       verb,
-		Args:       args,
-		Env:        cfg.Env,
-		BuildFlags: buildFlags,
-		WorkingDir: cfg.Dir,
-	}, cleanup, nil
+	return tmpURI, runner, inv, cleanup, nil
 }
 
 func (s *snapshot) buildOverlay() map[string][]byte {
diff --git a/internal/packagesinternal/packages.go b/internal/packagesinternal/packages.go
index 2c4527f..1335a5e 100644
--- a/internal/packagesinternal/packages.go
+++ b/internal/packagesinternal/packages.go
@@ -12,3 +12,6 @@
 var SetGoCmdRunner = func(config interface{}, runner *gocommand.Runner) {}
 
 var TypecheckCgo int
+
+var SetModFlag = func(config interface{}, value string) {}
+var SetModFile = func(config interface{}, value string) {}