diff --git a/gopls/internal/regtest/diagnostics_test.go b/gopls/internal/regtest/diagnostics_test.go
index 2d70f40..0291f2c 100644
--- a/gopls/internal/regtest/diagnostics_test.go
+++ b/gopls/internal/regtest/diagnostics_test.go
@@ -280,6 +280,23 @@
 			)
 		})
 	})
+
+	t.Run("without workspace module", func(t *testing.T) {
+		withOptions(EditorConfig{
+			WithoutExperimentalWorkspaceModule: true,
+		}).run(t, noMod, func(t *testing.T, env *Env) {
+			env.Await(
+				env.DiagnosticAtRegexp("main.go", `"mod.com/bob"`),
+			)
+			if err := env.Sandbox.RunGoCommand(env.Ctx, "", "mod", []string{"init", "mod.com"}); err != nil {
+				t.Fatal(err)
+			}
+			env.Await(
+				EmptyDiagnostics("main.go"),
+				env.DiagnosticAtRegexp("bob/bob.go", "x"),
+			)
+		})
+	})
 }
 
 // Tests golang/go#38267.
diff --git a/internal/lsp/cache/session.go b/internal/lsp/cache/session.go
index 44792f2..e597873 100644
--- a/internal/lsp/cache/session.go
+++ b/internal/lsp/cache/session.go
@@ -254,8 +254,9 @@
 	if !options.ExperimentalWorkspaceModule {
 		path := filepath.Join(root.Filename(), "go.mod")
 		if info, _ := os.Stat(path); info != nil {
-			m := newModule(ctx, span.URIFromPath(path))
-			modules[m.rootURI] = m
+			if m := getViewModule(ctx, root, span.URIFromPath(path), options); m != nil {
+				modules[m.rootURI] = m
+			}
 		}
 		return modules, nil
 	}
@@ -277,8 +278,9 @@
 		}
 		// We're only interested in go.mod files.
 		if filepath.Base(path) == "go.mod" {
-			m := newModule(ctx, span.URIFromPath(path))
-			modules[m.rootURI] = m
+			if m := getViewModule(ctx, root, span.URIFromPath(path), options); m != nil {
+				modules[m.rootURI] = m
+			}
 		}
 		return nil
 	})
diff --git a/internal/lsp/cache/snapshot.go b/internal/lsp/cache/snapshot.go
index d08bc78..4697bb3 100644
--- a/internal/lsp/cache/snapshot.go
+++ b/internal/lsp/cache/snapshot.go
@@ -1077,8 +1077,11 @@
 			rootURI := span.URIFromPath(filepath.Dir(withoutURI.Filename()))
 			if currentMod {
 				if _, ok := result.modules[rootURI]; !ok {
-					result.modules[rootURI] = newModule(ctx, currentFH.URI())
-					shouldReinitializeView = true
+					if m := getViewModule(ctx, s.view.rootURI, currentFH.URI(), s.view.options); m != nil {
+						result.modules[m.rootURI] = m
+						shouldReinitializeView = true
+					}
+
 				}
 			} else if originalMod {
 				// Similarly, we need to retry the IWL if a go.mod in the workspace
@@ -1574,8 +1577,15 @@
 	return file, nil
 }
 
-func newModule(ctx context.Context, modURI span.URI) *moduleRoot {
+func getViewModule(ctx context.Context, viewRootURI, modURI span.URI, options *source.Options) *moduleRoot {
 	rootURI := span.URIFromPath(filepath.Dir(modURI.Filename()))
+	// If we are not in multi-module mode, check that the affected module is
+	// in the workspace root.
+	if !options.ExperimentalWorkspaceModule {
+		if span.CompareURI(rootURI, viewRootURI) != 0 {
+			return nil
+		}
+	}
 	sumURI := span.URIFromPath(sumFilename(modURI))
 	if info, _ := os.Stat(sumURI.Filename()); info == nil {
 		sumURI = ""