diff --git a/internal/lsp/cache/snapshot.go b/internal/lsp/cache/snapshot.go
index b691ab3063..d916de3c35 100644
--- a/internal/lsp/cache/snapshot.go
+++ b/internal/lsp/cache/snapshot.go
@@ -694,7 +694,7 @@ func (s *snapshot) CachedImportPaths(ctx context.Context) (map[string]source.Pac
 func (s *snapshot) GoModForFile(ctx context.Context, uri span.URI) span.URI {
 	var match span.URI
 	for modURI := range s.workspace.activeModFiles() {
-		if !isSubdirectory(dirURI(modURI).Filename(), uri.Filename()) {
+		if !inDir(dirURI(modURI).Filename(), uri.Filename()) {
 			continue
 		}
 		if len(modURI) > len(match) {
@@ -1377,7 +1377,7 @@ func (s *snapshot) shouldInvalidateMetadata(ctx context.Context, newSnapshot *sn
 	}
 	// If a go.mod in the workspace has been changed, invalidate metadata.
 	if kind := originalFH.Kind(); kind == source.Mod {
-		return isSubdirectory(filepath.Dir(s.view.rootURI.Filename()), filepath.Dir(originalFH.URI().Filename()))
+		return inDir(filepath.Dir(s.view.rootURI.Filename()), filepath.Dir(originalFH.URI().Filename()))
 	}
 	// Get the original and current parsed files in order to check package name
 	// and imports. Use the new snapshot to parse to avoid modifying the
diff --git a/internal/lsp/cache/view.go b/internal/lsp/cache/view.go
index 84a5499efb..f27d8ca1af 100644
--- a/internal/lsp/cache/view.go
+++ b/internal/lsp/cache/view.go
@@ -698,16 +698,85 @@ func validBuildConfiguration(folder span.URI, ws *workspaceInformation, modFiles
 	// The user may have a multiple directories in their GOPATH.
 	// Check if the workspace is within any of them.
 	for _, gp := range filepath.SplitList(ws.gopath) {
-		if isSubdirectory(filepath.Join(gp, "src"), folder.Filename()) {
+		if inDir(filepath.Join(gp, "src"), folder.Filename()) {
 			return true
 		}
 	}
 	return false
 }
 
-func isSubdirectory(root, leaf string) bool {
-	rel, err := filepath.Rel(root, leaf)
-	return err == nil && !strings.HasPrefix(rel, "..")
+// Copied and slightly adjusted from go/src/cmd/go/internal/search/search.go.
+//
+// inDir checks whether path is in the file tree rooted at dir.
+// If so, InDir returns an equivalent path relative to dir.
+// If not, InDir returns an empty string.
+// InDir makes some effort to succeed even in the presence of symbolic links.
+func inDir(dir, path string) bool {
+	if rel := inDirLex(path, dir); rel != "" {
+		return true
+	}
+	xpath, err := filepath.EvalSymlinks(path)
+	if err != nil || xpath == path {
+		xpath = ""
+	} else {
+		if rel := inDirLex(xpath, dir); rel != "" {
+			return true
+		}
+	}
+
+	xdir, err := filepath.EvalSymlinks(dir)
+	if err == nil && xdir != dir {
+		if rel := inDirLex(path, xdir); rel != "" {
+			return true
+		}
+		if xpath != "" {
+			if rel := inDirLex(xpath, xdir); rel != "" {
+				return true
+			}
+		}
+	}
+	return false
+}
+
+// Copied from go/src/cmd/go/internal/search/search.go.
+//
+// inDirLex is like inDir but only checks the lexical form of the file names.
+// It does not consider symbolic links.
+// TODO(rsc): This is a copy of str.HasFilePathPrefix, modified to
+// return the suffix. Most uses of str.HasFilePathPrefix should probably
+// be calling InDir instead.
+func inDirLex(path, dir string) string {
+	pv := strings.ToUpper(filepath.VolumeName(path))
+	dv := strings.ToUpper(filepath.VolumeName(dir))
+	path = path[len(pv):]
+	dir = dir[len(dv):]
+	switch {
+	default:
+		return ""
+	case pv != dv:
+		return ""
+	case len(path) == len(dir):
+		if path == dir {
+			return "."
+		}
+		return ""
+	case dir == "":
+		return path
+	case len(path) > len(dir):
+		if dir[len(dir)-1] == filepath.Separator {
+			if path[:len(dir)] == dir {
+				return path[len(dir):]
+			}
+			return ""
+		}
+		if path[len(dir)] == filepath.Separator && path[:len(dir)] == dir {
+			if len(path) == len(dir)+1 {
+				return "."
+			}
+			return path[len(dir)+1:]
+		}
+		return ""
+	}
 }
 
 // getGoEnv gets the view's various GO* values.
diff --git a/internal/lsp/cache/workspace.go b/internal/lsp/cache/workspace.go
index 71d3842329..673843a57a 100644
--- a/internal/lsp/cache/workspace.go
+++ b/internal/lsp/cache/workspace.go
@@ -258,7 +258,7 @@ func (wm *workspace) invalidate(ctx context.Context, changes map[span.URI]*fileC
 				// Legacy mode only considers a module a workspace root.
 				continue
 			}
-			if !isSubdirectory(wm.root.Filename(), uri.Filename()) {
+			if !inDir(wm.root.Filename(), uri.Filename()) {
 				// Otherwise, the module must be contained within the workspace root.
 				continue
 			}