diff --git a/src/cmap/handshake/client_metadata.ts b/src/cmap/handshake/client_metadata.ts
index 0c00af9a8e..ab66328ca5 100644
--- a/src/cmap/handshake/client_metadata.ts
+++ b/src/cmap/handshake/client_metadata.ts
@@ -116,12 +116,12 @@ export function makeClientMetadata(options: MakeClientMetadataOptions): ClientMe
     );
   }
 
-  const platformInfo =
-    platform.length > 0
-      ? `Node.js ${process.version}, ${os.endianness()}|${platform}`
-      : `Node.js ${process.version}, ${os.endianness()}`;
+  let runtimeInfo = getRuntimeInfo();
+  if (platform.length > 0) {
+    runtimeInfo = `${runtimeInfo}|${platform}`;
+  }
 
-  if (!metadataDocument.ifItFitsItSits('platform', platformInfo)) {
+  if (!metadataDocument.ifItFitsItSits('platform', runtimeInfo)) {
     throw new MongoInvalidArgumentError(
       'Unable to include driverInfo platform, metadata cannot exceed 512 bytes'
     );
@@ -234,3 +234,39 @@ export function getFAASEnv(): Map<string, string | Int32> | null {
 
   return null;
 }
+
+/**
+ * @internal
+ * This type represents the global Deno object and the minimal type contract we expect it to satisfy.
+ */
+declare const Deno: { version?: { deno?: string } } | undefined;
+
+/**
+ * @internal
+ * This type represents the global Bun object and the minimal type contract we expect it to satisfy.
+ */
+declare const Bun: { (): void; version?: string } | undefined;
+
+/**
+ * @internal
+ * Get current JavaScript runtime platform
+ *
+ * NOTE: The version information fetching is intentionally written defensively
+ * to avoid having a released driver version that becomes incompatible
+ * with a future change to these global objects.
+ */
+function getRuntimeInfo(): string {
+  if ('Deno' in globalThis) {
+    const version = typeof Deno?.version?.deno === 'string' ? Deno?.version?.deno : '0.0.0-unknown';
+
+    return `Deno v${version}, ${os.endianness()}`;
+  }
+
+  if ('Bun' in globalThis) {
+    const version = typeof Bun?.version === 'string' ? Bun?.version : '0.0.0-unknown';
+
+    return `Bun v${version}, ${os.endianness()}`;
+  }
+
+  return `Node.js ${process.version}, ${os.endianness()}`;
+}
diff --git a/test/unit/cmap/handshake/client_metadata.test.ts b/test/unit/cmap/handshake/client_metadata.test.ts
index 83f51e89b1..3e96df7c6f 100644
--- a/test/unit/cmap/handshake/client_metadata.test.ts
+++ b/test/unit/cmap/handshake/client_metadata.test.ts
@@ -289,6 +289,94 @@ describe('client metadata module', () => {
         });
       });
     });
+
+    context('when globalThis indicates alternative runtime', () => {
+      context('deno', () => {
+        afterEach(() => {
+          expect(delete globalThis.Deno, 'failed to delete Deno global').to.be.true;
+        });
+
+        it('sets platform to Deno', () => {
+          globalThis.Deno = { version: { deno: '1.2.3' } };
+          const metadata = makeClientMetadata({ driverInfo: {} });
+          expect(metadata.platform).to.equal('Deno v1.2.3, LE');
+        });
+
+        it('sets platform to Deno with driverInfo.platform', () => {
+          globalThis.Deno = { version: { deno: '1.2.3' } };
+          const metadata = makeClientMetadata({ driverInfo: { platform: 'myPlatform' } });
+          expect(metadata.platform).to.equal('Deno v1.2.3, LE|myPlatform');
+        });
+
+        it('ignores version if Deno.version.deno is not a string', () => {
+          globalThis.Deno = { version: { deno: 1 } };
+          const metadata = makeClientMetadata({ driverInfo: {} });
+          expect(metadata.platform).to.equal('Deno v0.0.0-unknown, LE');
+        });
+
+        it('ignores version if Deno.version does not have a deno property', () => {
+          globalThis.Deno = { version: { somethingElse: '1.2.3' } };
+          const metadata = makeClientMetadata({ driverInfo: {} });
+          expect(metadata.platform).to.equal('Deno v0.0.0-unknown, LE');
+        });
+
+        it('ignores version if Deno.version is null', () => {
+          globalThis.Deno = { version: null };
+          const metadata = makeClientMetadata({ driverInfo: {} });
+          expect(metadata.platform).to.equal('Deno v0.0.0-unknown, LE');
+        });
+
+        it('ignores version if Deno is nullish', () => {
+          globalThis.Deno = null;
+          const metadata = makeClientMetadata({ driverInfo: {} });
+          expect(metadata.platform).to.equal('Deno v0.0.0-unknown, LE');
+        });
+      });
+
+      context('bun', () => {
+        afterEach(() => {
+          expect(delete globalThis.Bun, 'failed to delete Bun global').to.be.true;
+        });
+
+        it('sets platform to Bun', () => {
+          globalThis.Bun = class {
+            static version = '1.2.3';
+          };
+          const metadata = makeClientMetadata({ driverInfo: {} });
+          expect(metadata.platform).to.equal('Bun v1.2.3, LE');
+        });
+
+        it('sets platform to Bun with driverInfo.platform', () => {
+          globalThis.Bun = class {
+            static version = '1.2.3';
+          };
+          const metadata = makeClientMetadata({ driverInfo: { platform: 'myPlatform' } });
+          expect(metadata.platform).to.equal('Bun v1.2.3, LE|myPlatform');
+        });
+
+        it('ignores version if Bun.version is not a string', () => {
+          globalThis.Bun = class {
+            static version = 1;
+          };
+          const metadata = makeClientMetadata({ driverInfo: {} });
+          expect(metadata.platform).to.equal('Bun v0.0.0-unknown, LE');
+        });
+
+        it('ignores version if Bun.version is not a string and sets driverInfo.platform', () => {
+          globalThis.Bun = class {
+            static version = 1;
+          };
+          const metadata = makeClientMetadata({ driverInfo: { platform: 'myPlatform' } });
+          expect(metadata.platform).to.equal('Bun v0.0.0-unknown, LE|myPlatform');
+        });
+
+        it('ignores version if Bun is nullish', () => {
+          globalThis.Bun = null;
+          const metadata = makeClientMetadata({ driverInfo: { platform: 'myPlatform' } });
+          expect(metadata.platform).to.equal('Bun v0.0.0-unknown, LE|myPlatform');
+        });
+      });
+    });
   });
 
   describe('FAAS metadata application to handshake', () => {