diff --git a/src/vs/workbench/api/common/extHost.api.impl.ts b/src/vs/workbench/api/common/extHost.api.impl.ts
index 88ef2492dec..864b227de8e 100644
--- a/src/vs/workbench/api/common/extHost.api.impl.ts
+++ b/src/vs/workbench/api/common/extHost.api.impl.ts
@@ -91,7 +91,7 @@ import { ExtHostNotebookEditors } from 'vs/workbench/api/common/extHostNotebookE
 import { ExtHostNotebookDocuments } from 'vs/workbench/api/common/extHostNotebookDocuments';
 import { ExtHostInteractive } from 'vs/workbench/api/common/extHostInteractive';
 import { combinedDisposable } from 'vs/base/common/lifecycle';
-import { checkProposedApiEnabled, isProposedApiEnabled } from 'vs/workbench/services/extensions/common/extensions';
+import { checkProposedApiEnabled, ExtensionIdentifierSet, isProposedApiEnabled } from 'vs/workbench/services/extensions/common/extensions';
 import { DebugConfigurationProviderTriggerKind } from 'vs/workbench/contrib/debug/common/debug';
 import { ExtHostNotebookProxyKernels } from 'vs/workbench/api/common/extHostNotebookProxyKernels';
 
@@ -419,12 +419,11 @@ export function createApiFactoryAndRegisterActors(accessor: ServicesAccessor): I
 			},
 			get allAcrossExtensionHosts(): vscode.Extension<any>[] {
 				checkProposedApiEnabled(extension, 'extensionsAny');
+				const local = new ExtensionIdentifierSet(extensionInfo.mine.getAllExtensionDescriptions().map(desc => desc.identifier));
 				const result: vscode.Extension<any>[] = [];
-				for (const desc of extensionInfo.mine.getAllExtensionDescriptions()) {
-					result.push(new Extension(extensionService, extension.identifier, desc, extensionKind, false));
-				}
 				for (const desc of extensionInfo.all.getAllExtensionDescriptions()) {
-					result.push(new Extension(extensionService, extension.identifier, desc, extensionKind /* TODO@alexdima THIS IS WRONG */, true));
+					const isFromDifferentExtensionHost = !local.has(desc.identifier);
+					result.push(new Extension(extensionService, extension.identifier, desc, extensionKind /* TODO@alexdima THIS IS WRONG */, isFromDifferentExtensionHost));
 				}
 				return result;
 			},
diff --git a/src/vs/workbench/services/extensions/common/extensions.ts b/src/vs/workbench/services/extensions/common/extensions.ts
index 1a564e9a491..722dba8dd6b 100644
--- a/src/vs/workbench/services/extensions/common/extensions.ts
+++ b/src/vs/workbench/services/extensions/common/extensions.ts
@@ -283,6 +283,65 @@ export class ExtensionHostExtensions {
 	}
 }
 
+export class ExtensionIdentifierSet implements Set<ExtensionIdentifier> {
+
+	readonly [Symbol.toStringTag]: string = 'ExtensionIdentifierSet';
+
+	private readonly _map = new Map<string, ExtensionIdentifier>();
+	private readonly _toKey = ExtensionIdentifier.toKey;
+
+	constructor(values?: Iterable<ExtensionIdentifier>) {
+		if (values) {
+			for (const value of values) {
+				this.add(value);
+			}
+		}
+	}
+
+	get size(): number {
+		return this._map.size;
+	}
+
+	add(value: ExtensionIdentifier): this {
+		this._map.set(this._toKey(value), value);
+		return this;
+	}
+
+	clear(): void {
+		this._map.clear();
+	}
+
+	delete(value: ExtensionIdentifier): boolean {
+		return this._map.delete(this._toKey(value));
+	}
+
+	has(value: ExtensionIdentifier): boolean {
+		return this._map.has(this._toKey(value));
+	}
+
+	forEach(callbackfn: (value: ExtensionIdentifier, value2: ExtensionIdentifier, set: Set<ExtensionIdentifier>) => void, thisArg?: any): void {
+		this._map.forEach(value => callbackfn.call(thisArg, value, value, this));
+	}
+
+	*entries(): IterableIterator<[ExtensionIdentifier, ExtensionIdentifier]> {
+		for (let [_key, value] of this._map) {
+			yield [value, value];
+		}
+	}
+
+	keys(): IterableIterator<ExtensionIdentifier> {
+		return this._map.values();
+	}
+
+	values(): IterableIterator<ExtensionIdentifier> {
+		return this._map.values();
+	}
+
+	[Symbol.iterator](): IterableIterator<ExtensionIdentifier> {
+		return this._map.values();
+	}
+}
+
 export function extensionIdentifiersArrayToSet(extensionIds: ExtensionIdentifier[]): Set<string> {
 	const result = new Set<string>();
 	for (const extensionId of extensionIds) {