diff --git a/packages/node-core/src/integrations/http/SentryHttpInstrumentation.ts b/packages/node-core/src/integrations/http/SentryHttpInstrumentation.ts
index b25d32138aa9..60cf7bbae9aa 100644
--- a/packages/node-core/src/integrations/http/SentryHttpInstrumentation.ts
+++ b/packages/node-core/src/integrations/http/SentryHttpInstrumentation.ts
@@ -456,10 +456,16 @@ function _getOutgoingRequestSpanData(request: http.ClientRequest): [string, Span
   ];
 }
 
-function _getOutgoingRequestEndedSpanData(response: http.IncomingMessage): SpanAttributes {
+/**
+ * Exported for testing purposes.
+ */
+export function _getOutgoingRequestEndedSpanData(response: http.IncomingMessage): SpanAttributes {
   const { statusCode, statusMessage, httpVersion, socket } = response;
 
-  const transport = httpVersion.toUpperCase() !== 'QUIC' ? 'ip_tcp' : 'ip_udp';
+  // httpVersion can be undefined in some cases and we seem to have encountered this before:
+  // https://github.com/getsentry/sentry-javascript/blob/ec8c8c64cde6001123db0199a8ca017b8863eac8/packages/node-core/src/integrations/http/httpServerSpansIntegration.ts#L158
+  // see: #20415
+  const transport = httpVersion?.toUpperCase() !== 'QUIC' ? 'ip_tcp' : 'ip_udp';
 
   const additionalAttributes: SpanAttributes = {
     [ATTR_HTTP_RESPONSE_STATUS_CODE]: statusCode,
diff --git a/packages/node-core/test/integrations/SentryHttpInstrumentation.test.ts b/packages/node-core/test/integrations/SentryHttpInstrumentation.test.ts
new file mode 100644
index 000000000000..182abaa3663f
--- /dev/null
+++ b/packages/node-core/test/integrations/SentryHttpInstrumentation.test.ts
@@ -0,0 +1,48 @@
+import type * as http from 'node:http';
+import { describe, expect, it } from 'vitest';
+import { _getOutgoingRequestEndedSpanData } from '../../src/integrations/http/SentryHttpInstrumentation';
+
+function createResponse(overrides: Partial<http.IncomingMessage>): http.IncomingMessage {
+  return {
+    statusCode: 200,
+    statusMessage: 'OK',
+    httpVersion: '1.1',
+    headers: {},
+    socket: undefined,
+    ...overrides,
+  } as unknown as http.IncomingMessage;
+}
+
+describe('_getOutgoingRequestEndedSpanData', () => {
+  it('sets ip_tcp transport for HTTP/1.1', () => {
+    const attributes = _getOutgoingRequestEndedSpanData(createResponse({ httpVersion: '1.1' }));
+
+    expect(attributes['network.transport']).toBe('ip_tcp');
+    expect(attributes['net.transport']).toBe('ip_tcp');
+    expect(attributes['network.protocol.version']).toBe('1.1');
+    expect(attributes['http.flavor']).toBe('1.1');
+  });
+
+  it('sets ip_udp transport for QUIC', () => {
+    const attributes = _getOutgoingRequestEndedSpanData(createResponse({ httpVersion: 'QUIC' }));
+
+    expect(attributes['network.transport']).toBe('ip_udp');
+    expect(attributes['net.transport']).toBe('ip_udp');
+  });
+
+  it('does not throw when httpVersion is null', () => {
+    expect(() =>
+      _getOutgoingRequestEndedSpanData(createResponse({ httpVersion: null as unknown as string })),
+    ).not.toThrow();
+
+    const attributes = _getOutgoingRequestEndedSpanData(createResponse({ httpVersion: null as unknown as string }));
+    expect(attributes['network.transport']).toBe('ip_tcp');
+    expect(attributes['net.transport']).toBe('ip_tcp');
+  });
+
+  it('does not throw when httpVersion is undefined', () => {
+    expect(() =>
+      _getOutgoingRequestEndedSpanData(createResponse({ httpVersion: undefined as unknown as string })),
+    ).not.toThrow();
+  });
+});