diff --git a/internal/lsp/cache/modfiles.go b/internal/lsp/cache/modfiles.go
index 63403d01e1c..d45a5ca9db9 100644
--- a/internal/lsp/cache/modfiles.go
+++ b/internal/lsp/cache/modfiles.go
@@ -20,16 +20,19 @@ import (
 // This function will return the main go.mod file for this folder if it exists and whether the -modfile
 // flag exists for this version of go.
 func modfileFlagExists(ctx context.Context, folder string, env []string) (string, bool, error) {
-	// Borrowed from (internal/imports/mod.go:620)
+	// Check the Go version by running go list with GO111MODULE=off.
+	// If the output is anything other than "go1.14\n", assume -modfile is not supported.
+	// Borrowed from internal/imports/mod.go:620
 	const format = `{{range context.ReleaseTags}}{{if eq . "go1.14"}}{{.}}{{end}}{{end}}`
-	// Check the go version by running "go list" with modules off.
-	stdout, err := source.InvokeGo(ctx, folder, append(env, "GO111MODULE=off"), "list", "-f", format)
+	stdout, err := source.InvokeGo(ctx, folder, append(env, "GO111MODULE=off"), "list", "-e", "-f", format)
 	if err != nil {
 		return "", false, err
 	}
+	// If the output is not go1.14 or an empty string, then it could be an error.
 	lines := strings.Split(stdout.String(), "\n")
-	if len(lines) < 2 {
-		return "", false, errors.Errorf("unexpected stdout: %q", stdout)
+	if len(lines) < 2 && stdout.String() != "" {
+		log.Error(ctx, "unexpected stdout when checking for go1.14", errors.Errorf("%q", stdout), telemetry.Directory.Of(folder))
+		return "", false, nil
 	}
 	// Get the go.mod file associated with this module.
 	b, err := source.InvokeGo(ctx, folder, env, "env", "GOMOD")
diff --git a/internal/lsp/diagnostics.go b/internal/lsp/diagnostics.go
index b359ecf87d4..3e5068ef139 100644
--- a/internal/lsp/diagnostics.go
+++ b/internal/lsp/diagnostics.go
@@ -69,15 +69,14 @@ func (s *Server) diagnoseModfile(snapshot source.Snapshot) {
 	ctx, done := trace.StartSpan(ctx, "lsp:background-worker")
 	defer done()
 
-	f, diags, err := mod.Diagnostics(ctx, snapshot)
+	reports, err := mod.Diagnostics(ctx, snapshot)
 	if err != nil {
 		if err != context.Canceled {
 			log.Error(ctx, "diagnoseModfile: could not generate diagnostics", err)
 		}
 		return
 	}
-	reports := map[source.FileIdentity][]source.Diagnostic{f: diags}
-	// Publish empty diagnostics for files.
+	// Publish empty diagnostics for go.mod files.
 	s.publishReports(ctx, reports, true)
 }
 
diff --git a/internal/lsp/mod/diagnostics.go b/internal/lsp/mod/diagnostics.go
index 2d8b04e7f54..850411f94fb 100644
--- a/internal/lsp/mod/diagnostics.go
+++ b/internal/lsp/mod/diagnostics.go
@@ -18,15 +18,15 @@ import (
 	"golang.org/x/tools/internal/telemetry/trace"
 )
 
-func Diagnostics(ctx context.Context, snapshot source.Snapshot) (source.FileIdentity, []source.Diagnostic, error) {
+func Diagnostics(ctx context.Context, snapshot source.Snapshot) (map[source.FileIdentity][]source.Diagnostic, error) {
 	// TODO: We will want to support diagnostics for go.mod files even when the -modfile flag is turned off.
 	realfh, tempfh, err := snapshot.ModFiles(ctx)
 	if err != nil {
-		return source.FileIdentity{}, nil, err
+		return nil, err
 	}
 	// Check the case when the tempModfile flag is turned off.
 	if realfh == nil || tempfh == nil {
-		return source.FileIdentity{}, nil, nil
+		return nil, nil
 	}
 
 	ctx, done := trace.StartSpan(ctx, "modfiles.Diagnostics", telemetry.File.Of(realfh.Identity().URI))
@@ -39,31 +39,34 @@ func Diagnostics(ctx context.Context, snapshot source.Snapshot) (source.FileIden
 	if _, err := source.InvokeGo(ctx, snapshot.View().Folder().Filename(), cfg.Env, args...); err != nil {
 		// Ignore parse errors here. They'll be handled below.
 		if !strings.Contains(err.Error(), "errors parsing go.mod") {
-			return source.FileIdentity{}, nil, err
+			return nil, err
 		}
 	}
 
 	realMod, err := snapshot.View().Session().Cache().ParseModHandle(realfh).Parse(ctx)
+	// If the go.mod file fails to parse, return errors right away.
 	if err, ok := err.(*source.Error); ok {
-		return realfh.Identity(), []source.Diagnostic{
-			{
+		return map[source.FileIdentity][]source.Diagnostic{
+			realfh.Identity(): []source.Diagnostic{{
 				Message:  err.Message,
-				Source:   "go mod tidy",
+				Source:   "syntax",
 				Range:    err.Range,
 				Severity: protocol.SeverityError,
-			},
+			}},
 		}, nil
 	}
 	if err != nil {
-		return source.FileIdentity{}, nil, err
+		return nil, err
 	}
 	tempMod, err := snapshot.View().Session().Cache().ParseModHandle(tempfh).Parse(ctx)
 	if err != nil {
-		return source.FileIdentity{}, nil, err
+		return nil, err
 	}
 
 	// Check indirect vs direct, and removal of dependencies.
-	reports := []source.Diagnostic{}
+	reports := map[source.FileIdentity][]source.Diagnostic{
+		realfh.Identity(): []source.Diagnostic{},
+	}
 	realReqs := make(map[string]*modfile.Require, len(realMod.Require))
 	tempReqs := make(map[string]*modfile.Require, len(tempMod.Require))
 	for _, req := range realMod.Require {
@@ -93,9 +96,9 @@ func Diagnostics(ctx context.Context, snapshot source.Snapshot) (source.FileIden
 				diag.Message = fmt.Sprintf("%s should not be an indirect dependency.", dep)
 			}
 		}
-		reports = append(reports, *diag)
+		reports[realfh.Identity()] = append(reports[realfh.Identity()], *diag)
 	}
-	return realfh.Identity(), reports, nil
+	return reports, nil
 }
 
 // TODO: Check to see if we need to go through internal/span (for multiple byte characters).
diff --git a/internal/lsp/mod/mod_test.go b/internal/lsp/mod/mod_test.go
index 8f2e17c1949..76ed109a06f 100644
--- a/internal/lsp/mod/mod_test.go
+++ b/internal/lsp/mod/mod_test.go
@@ -108,7 +108,7 @@ func TestDiagnostics(t *testing.T) {
 			want: []source.Diagnostic{
 				{
 					Message:  "usage: require module/path v1.2.3",
-					Source:   "go mod tidy",
+					Source:   "syntax",
 					Range:    protocol.Range{Start: getPos(4, 0), End: getPos(4, 17)},
 					Severity: protocol.SeverityError,
 				},
@@ -119,7 +119,7 @@ func TestDiagnostics(t *testing.T) {
 			want: []source.Diagnostic{
 				{
 					Message:  "usage: go 1.23",
-					Source:   "go mod tidy",
+					Source:   "syntax",
 					Range:    protocol.Range{Start: getPos(2, 0), End: getPos(2, 4)},
 					Severity: protocol.SeverityError,
 				},
@@ -130,7 +130,7 @@ func TestDiagnostics(t *testing.T) {
 			want: []source.Diagnostic{
 				{
 					Message:  "unknown directive: yo",
-					Source:   "go mod tidy",
+					Source:   "syntax",
 					Range:    protocol.Range{Start: getPos(6, 0), End: getPos(6, 2)},
 					Severity: protocol.SeverityError,
 				},
@@ -153,12 +153,17 @@ func TestDiagnostics(t *testing.T) {
 			if !hasTempModfile(ctx, snapshot) {
 				return
 			}
-			fileID, got, err := mod.Diagnostics(ctx, snapshot)
+			reports, err := mod.Diagnostics(ctx, snapshot)
 			if err != nil {
 				t.Fatal(err)
 			}
-			if diff := tests.DiffDiagnostics(fileID.URI, tt.want, got); diff != "" {
-				t.Error(diff)
+			if len(reports) != 1 {
+				t.Errorf("expected 1 fileHandle, got %d", len(reports))
+			}
+			for fh, got := range reports {
+				if diff := tests.DiffDiagnostics(fh.URI, tt.want, got); diff != "" {
+					t.Error(diff)
+				}
 			}
 		})
 	}