diff --git a/gopls/internal/regtest/workspace/workspace_test.go b/gopls/internal/regtest/workspace/workspace_test.go
index 11ab507708..666f023ace 100644
--- a/gopls/internal/regtest/workspace/workspace_test.go
+++ b/gopls/internal/regtest/workspace/workspace_test.go
@@ -855,6 +855,7 @@ func TestWorkspaceDirAccess(t *testing.T) {
 -- moda/a/go.mod --
 module a.com
 
+go 1.15
 -- moda/a/a.go --
 package main
 
@@ -863,6 +864,8 @@ func main() {
 }
 -- modb/go.mod --
 module b.com
+
+go 1.16
 -- modb/b/b.go --
 package main
 
@@ -892,7 +895,7 @@ func main() {
 			t.Fatalf("reading expected workspace modfile: %v", err)
 		}
 		got := string(gotb)
-		for _, want := range []string{"a.com v1.9999999.0-goplsworkspace", "b.com v1.9999999.0-goplsworkspace"} {
+		for _, want := range []string{"go 1.16", "a.com v1.9999999.0-goplsworkspace", "b.com v1.9999999.0-goplsworkspace"} {
 			if !strings.Contains(got, want) {
 				// want before got here, since the go.mod is multi-line
 				t.Fatalf("workspace go.mod missing %q. got:\n%s", want, got)
diff --git a/internal/lsp/cache/snapshot.go b/internal/lsp/cache/snapshot.go
index 486a2287cd..51b00d5b61 100644
--- a/internal/lsp/cache/snapshot.go
+++ b/internal/lsp/cache/snapshot.go
@@ -2290,7 +2290,8 @@ func buildWorkspaceModFile(ctx context.Context, modFiles map[span.URI]struct{},
 		if file == nil || parsed.Module == nil {
 			return nil, fmt.Errorf("no module declaration for %s", modURI)
 		}
-		if parsed.Go != nil && semver.Compare(goVersion, parsed.Go.Version) < 0 {
+		// Prepend "v" to go versions to make them valid semver.
+		if parsed.Go != nil && semver.Compare("v"+goVersion, "v"+parsed.Go.Version) < 0 {
 			goVersion = parsed.Go.Version
 		}
 		path := parsed.Module.Mod.Path