diff --git a/src/cmd/go/internal/modindex/read.go b/src/cmd/go/internal/modindex/read.go
index 38ddfec70f..707f17e1ab 100644
--- a/src/cmd/go/internal/modindex/read.go
+++ b/src/cmd/go/internal/modindex/read.go
@@ -139,6 +139,9 @@ func GetPackage(modroot, pkgdir string) (*IndexPackage, error) {
 	if !errors.Is(err, errNotFromModuleCache) {
 		return nil, err
 	}
+	if cfg.BuildContext.Compiler == "gccgo" && str.HasPathPrefix(modroot, cfg.GOROOTsrc) {
+		return nil, err // gccgo has no sources for GOROOT packages.
+	}
 	return openIndexPackage(modroot, pkgdir)
 }
 
diff --git a/src/go/build/build.go b/src/go/build/build.go
index bfe3f444ca..dfb37b8f34 100644
--- a/src/go/build/build.go
+++ b/src/go/build/build.go
@@ -715,6 +715,9 @@ func (ctxt *Context) Import(path string, srcDir string, mode ImportMode) (*Packa
 				tried.goroot = dir
 			}
 			if ctxt.Compiler == "gccgo" && goroot.IsStandardPackage(ctxt.GOROOT, ctxt.Compiler, path) {
+				// TODO(bcmills): Setting p.Dir here is misleading, because gccgo
+				// doesn't actually load its standard-library packages from this
+				// directory. See if we can leave it unset.
 				p.Dir = ctxt.joinPath(ctxt.GOROOT, "src", path)
 				p.Goroot = true
 				p.Root = ctxt.GOROOT