diff --git a/libwvdrmengine/oemcrypto/test/oemcrypto_test.cpp b/libwvdrmengine/oemcrypto/test/oemcrypto_test.cpp
index 06144d70..f8a0d1cb 100644
--- a/libwvdrmengine/oemcrypto/test/oemcrypto_test.cpp
+++ b/libwvdrmengine/oemcrypto/test/oemcrypto_test.cpp
@@ -5719,19 +5719,29 @@ class OEMCryptoUsageTableDefragTest : public OEMCryptoUsageTableTest {
 
   void ShrinkHeader(uint32_t new_size,
                     OEMCryptoResult expected_result = OEMCrypto_SUCCESS) {
+    // We call OEMCrypto_ShrinkUsageTableHeader once with a zero length buffer,
+    // so that OEMCrypto can tell us how big the buffer should be.
     size_t header_buffer_length = 0;
     OEMCryptoResult sts = OEMCrypto_ShrinkUsageTableHeader(
         new_size, nullptr, &header_buffer_length);
+    // If we are expecting success, then the first call shall return
+    // SHORT_BUFFER. However, if we are not expecting success, this first call
+    // may return either SHORT_BUFFER or the expect error.
     if (expected_result == OEMCrypto_SUCCESS) {
       ASSERT_EQ(OEMCrypto_ERROR_SHORT_BUFFER, sts);
-    } else {
-      ASSERT_NE(OEMCrypto_SUCCESS, sts);
-      if (sts != OEMCrypto_ERROR_SHORT_BUFFER) return;
+    } else if (sts != OEMCrypto_ERROR_SHORT_BUFFER) {
+      // If we got any thing from the first call, it should be the expected
+      // error, and we don't need to call a second time.
+      ASSERT_EQ(expected_result, sts);
+      return;
     }
+    // If the first call resulted in SHORT_BUFFER, we should resize the buffer
+    // and try again.
     ASSERT_LT(0u, header_buffer_length);
     encrypted_usage_header_.resize(header_buffer_length);
     sts = OEMCrypto_ShrinkUsageTableHeader(
         new_size, encrypted_usage_header_.data(), &header_buffer_length);
+    // For the second call, we always demand the expected result.
     ASSERT_EQ(expected_result, sts);
   }
 };