diff --git a/internal/lsp/cache/external.go b/internal/lsp/cache/external.go
index b52899ba7f..7a938a2f4c 100644
--- a/internal/lsp/cache/external.go
+++ b/internal/lsp/cache/external.go
@@ -15,6 +15,9 @@ import (
 	"golang.org/x/tools/internal/span"
 )
 
+// ioLimit limits the number of parallel file reads per process.
+var ioLimit = make(chan struct{}, 128)
+
 // nativeFileSystem implements FileSystem reading from the normal os file system.
 type nativeFileSystem struct{}
 
@@ -54,6 +57,8 @@ func (h *nativeFileHandle) Kind() source.FileKind {
 func (h *nativeFileHandle) Read(ctx context.Context) ([]byte, string, error) {
 	ctx, done := trace.StartSpan(ctx, "cache.nativeFileHandle.Read", telemetry.File.Of(h.identity.URI.Filename()))
 	defer done()
+	ioLimit <- struct{}{}
+	defer func() { <-ioLimit }()
 	//TODO: this should fail if the version is not the same as the handle
 	data, err := ioutil.ReadFile(h.identity.URI.Filename())
 	if err != nil {
diff --git a/internal/lsp/cache/parse.go b/internal/lsp/cache/parse.go
index 3da4a6f238..8e9def8740 100644
--- a/internal/lsp/cache/parse.go
+++ b/internal/lsp/cache/parse.go
@@ -20,8 +20,8 @@ import (
 	errors "golang.org/x/xerrors"
 )
 
-// Limits the number of parallel file reads per process.
-var ioLimit = make(chan struct{}, 20)
+// Limits the number of parallel parser calls per process.
+var parseLimit = make(chan struct{}, 20)
 
 // parseKey uniquely identifies a parsed Go file.
 type parseKey struct {
@@ -104,13 +104,12 @@ func parseGo(ctx context.Context, c *cache, fh source.FileHandle, mode source.Pa
 	ctx, done := trace.StartSpan(ctx, "cache.parseGo", telemetry.File.Of(fh.Identity().URI.Filename()))
 	defer done()
 
-	ioLimit <- struct{}{}
 	buf, _, err := fh.Read(ctx)
-	<-ioLimit
 	if err != nil {
 		return nil, err
 	}
-
+	parseLimit <- struct{}{}
+	defer func() { <-parseLimit }()
 	parserMode := parser.AllErrors | parser.ParseComments
 	if mode == source.ParseHeader {
 		parserMode = parser.ImportsOnly | parser.ParseComments