diff --git a/internal/lsp/cmd/cmd.go b/internal/lsp/cmd/cmd.go
index 41c2bce2a2..fdaf6d1abc 100644
--- a/internal/lsp/cmd/cmd.go
+++ b/internal/lsp/cmd/cmd.go
@@ -504,13 +504,9 @@ func (c *connection) AddFile(ctx context.Context, uri span.URI) *cmdFile {
 	return file
 }
 
-func (c *connection) semanticTokens(ctx context.Context, file span.URI) (*protocol.SemanticTokens, error) {
-	p := &protocol.SemanticTokensParams{
-		TextDocument: protocol.TextDocumentIdentifier{
-			URI: protocol.URIFromSpanURI(file),
-		},
-	}
-	resp, err := c.Server.SemanticTokensFull(ctx, p)
+func (c *connection) semanticTokens(ctx context.Context, p *protocol.SemanticTokensRangeParams) (*protocol.SemanticTokens, error) {
+	// use range to avoid limits on full
+	resp, err := c.Server.SemanticTokensRange(ctx, p)
 	if err != nil {
 		return nil, err
 	}
diff --git a/internal/lsp/cmd/semantictokens.go b/internal/lsp/cmd/semantictokens.go
index 41e353cc8f..e8f9018c7d 100644
--- a/internal/lsp/cmd/semantictokens.go
+++ b/internal/lsp/cmd/semantictokens.go
@@ -94,13 +94,24 @@ func (c *semtok) Run(ctx context.Context, args ...string) error {
 		return file.err
 	}
 
-	resp, err := conn.semanticTokens(ctx, uri)
+	buf, err := ioutil.ReadFile(args[0])
 	if err != nil {
 		return err
 	}
-	buf, err := ioutil.ReadFile(args[0])
+	lines := bytes.Split(buf, []byte{'\n'})
+	p := &protocol.SemanticTokensRangeParams{
+		TextDocument: protocol.TextDocumentIdentifier{
+			URI: protocol.URIFromSpanURI(uri),
+		},
+		Range: protocol.Range{Start: protocol.Position{Line: 0, Character: 0},
+			End: protocol.Position{
+				Line:      uint32(len(lines) - 1),
+				Character: uint32(len(lines[len(lines)-1]))},
+		},
+	}
+	resp, err := conn.semanticTokens(ctx, p)
 	if err != nil {
-		log.Fatal(err)
+		return err
 	}
 	fset := token.NewFileSet()
 	f, err := parser.ParseFile(fset, args[0], buf, 0)
diff --git a/internal/lsp/semantic.go b/internal/lsp/semantic.go
index fbca581e49..8230a7c46c 100644
--- a/internal/lsp/semantic.go
+++ b/internal/lsp/semantic.go
@@ -22,6 +22,8 @@ import (
 	errors "golang.org/x/xerrors"
 )
 
+const maxFullFileSize int = 100000 // reject full semantic token requests for large files
+
 func (s *Server) semanticTokensFull(ctx context.Context, p *protocol.SemanticTokensParams) (*protocol.SemanticTokens, error) {
 	ret, err := s.computeSemanticTokens(ctx, p.TextDocument, nil)
 	return ret, err
@@ -68,6 +70,11 @@ func (s *Server) computeSemanticTokens(ctx context.Context, td protocol.TextDocu
 	if pgf.ParseErr != nil {
 		return nil, pgf.ParseErr
 	}
+	if rng == nil && len(pgf.Src) > maxFullFileSize {
+		err := fmt.Errorf("semantic tokens: file %s too large for full (%d>%d)",
+			td.URI.SpanURI().Filename(), len(pgf.Src), maxFullFileSize)
+		return nil, err
+	}
 	e := &encoded{
 		ctx:      ctx,
 		pgf:      pgf,
@@ -491,7 +498,7 @@ func (e *encoded) init() error {
 	}
 	span, err := e.pgf.Mapper.RangeSpan(*e.rng)
 	if err != nil {
-		return errors.Errorf("range span error for %s", e.pgf.File.Name)
+		return errors.Errorf("range span (%v) error for %s", err, e.pgf.File.Name)
 	}
 	e.end = e.start + token.Pos(span.End().Offset())
 	e.start += token.Pos(span.Start().Offset())