diff --git a/google-auth-library-java/oauth2_http/javatests/com/google/auth/oauth2/GoogleCredentialsTest.java b/google-auth-library-java/oauth2_http/javatests/com/google/auth/oauth2/GoogleCredentialsTest.java
index 74aa9fae9ccd..b97f3c05c0fa 100644
--- a/google-auth-library-java/oauth2_http/javatests/com/google/auth/oauth2/GoogleCredentialsTest.java
+++ b/google-auth-library-java/oauth2_http/javatests/com/google/auth/oauth2/GoogleCredentialsTest.java
@@ -122,6 +122,18 @@ void fromStream_unknownType_throws() throws IOException {
     }
   }
 
+  @Test
+  void fromStream_invalidJson_throws() throws IOException {
+    // Other client libraries (like Python, Go, and Rust) strictly validate JSON syntax and reject
+    // malformed payload structures immediately. This test ensures Java maintains parity by
+    // successfully throwing an IOException when ADC JSON parsing fails, preventing silent fallbacks.
+    MockHttpTransportFactory transportFactory = new MockHttpTransportFactory();
+    try (InputStream stream = new ByteArrayInputStream("invalid-json{".getBytes(java.nio.charset.StandardCharsets.UTF_8))) {
+      assertThrows(
+          IOException.class, () -> GoogleCredentials.fromStream(stream, transportFactory));
+    }
+  }
+
   @Test
   void fromStream_nullTransport_throws() {
     InputStream stream = new ByteArrayInputStream("foo".getBytes());