diff --git a/src/components/workspace-source-state.test.ts b/src/components/workspace-source-state.test.ts
index bfd0273..5345646 100644
--- a/src/components/workspace-source-state.test.ts
+++ b/src/components/workspace-source-state.test.ts
@@ -28,7 +28,7 @@ describe("workspaceSourceState", () => {
     );
   });
 
-  it("can select an unmaterialized Official Library row for preview", () => {
+  it("skips unmaterialized Official Library rows when choosing the initial Source", () => {
     const sources: readonly SourceView[] = [
       {
         id: "demo-spacex-s1",
@@ -54,10 +54,43 @@ describe("workspaceSourceState", () => {
     ];
 
     expect(workspaceSourceState.getInitialSelectedSourceId(sources)).toBe(
-      "demo-spacex-s1",
+      "source_ready",
     );
   });
 
+  it("does not resolve an unmaterialized Official Library row as the selected Source", () => {
+    const sources: readonly SourceView[] = [
+      {
+        id: "demo-spacex-s1",
+        kind: "demo",
+        demoSourceId: "demo-spacex-s1",
+        title: "spacex-s1.pdf",
+        status: "ready",
+        mimeType: "application/pdf",
+        excludedFromQuery: false,
+        officialLibrary: {
+          librarySourceId: "financial-spacex-s1",
+          categoryId: "financial-reports",
+          sourceUrl: "https://example.com/spacex-s1.pdf",
+        },
+      },
+      {
+        id: "source_ready",
+        title: "ready.pdf",
+        status: "ready",
+        mimeType: "application/pdf",
+        excludedFromQuery: false,
+      },
+    ];
+
+    expect(
+      workspaceSourceState.getResolvedSelectedSourceId(
+        sources,
+        "demo-spacex-s1",
+      ),
+    ).toBeNull();
+  });
+
   it("selects a preferred document source when opening a chunk-tree link", () => {
     const sources: readonly SourceView[] = [
       {
diff --git a/src/components/workspace-source-state.ts b/src/components/workspace-source-state.ts
index 97c0c55..5d33744 100644
--- a/src/components/workspace-source-state.ts
+++ b/src/components/workspace-source-state.ts
@@ -53,7 +53,8 @@ function getInitialSelectedSourceId(
   if (preferredDocumentId) {
     const preferredSource = sources.find(
       (source) =>
-        source.documentId === preferredDocumentId && isReadySource(source),
+        source.documentId === preferredDocumentId &&
+        isReadyVisibleSource(source),
     )
     if (preferredSource) return preferredSource.id
   }
@@ -62,7 +63,7 @@ function getInitialSelectedSourceId(
 }
 
 function getFirstReadySourceId(sources: readonly SourceView[]): string | null {
-  return sources.find(isReadySource)?.id ?? null
+  return sources.find(isReadyVisibleSource)?.id ?? null
 }
 
 function getResolvedSelectedSourceId(
@@ -73,14 +74,15 @@ function getResolvedSelectedSourceId(
 
   const selectedSource = sources.find((source) => source.id === selectedSourceId)
   if (selectedSource) {
-    return selectedSource.id
+    return isVisibleSource(selectedSource) ? selectedSource.id : null
   }
 
   const selectedDocumentId = getRemoteSourceDocumentId(selectedSourceId)
   if (selectedDocumentId) {
     const localizedSource = sources.find(
       (source) =>
-        source.documentId === selectedDocumentId && isReadySource(source),
+        source.documentId === selectedDocumentId &&
+        isReadyVisibleSource(source),
     )
     if (localizedSource) return localizedSource.id
   }
@@ -92,6 +94,14 @@ function isReadySource(source: SourceView): boolean {
   return source.status === "ready"
 }
 
+function isReadyVisibleSource(source: SourceView): boolean {
+  return isReadySource(source) && isVisibleSource(source)
+}
+
+function isVisibleSource(source: SourceView): boolean {
+  return source.officialLibrary === undefined
+}
+
 function applyQueryExclusions(
   sources: readonly SourceView[],
   sourceExclusionById: SourceExclusionState,