diff --git a/php/tests/BinaryFidelityTest.php b/php/tests/BinaryFidelityTest.php
index 9253cf5..6d267d4 100644
--- a/php/tests/BinaryFidelityTest.php
+++ b/php/tests/BinaryFidelityTest.php
@@ -43,7 +43,7 @@ class BinaryFidelityTest extends TestCase
         );
 
         $failures = [];
-        $identicalCount = 0;
+        $byteIdenticalCount = 0;
 
         foreach ($paths as $path) {
             $original = @file_get_contents($path);
@@ -66,25 +66,37 @@ class BinaryFidelityTest extends TestCase
             $reencoded = $presentation->serializeToString();
 
             if ($original === $reencoded) {
-                $identicalCount++;
+                $byteIdenticalCount++;
+            }
+
+            $roundTrip = new Presentation();
+            try {
+                $roundTrip->mergeFromString($reencoded);
+            } catch (\Throwable $throwable) {
+                $failures[] = [
+                    'path' => $path,
+                    'reason' => 'reencode_decode_error',
+                    'message' => $throwable->getMessage(),
+                ];
+
                 continue;
             }
 
-            $firstMismatch = $this->firstMismatchOffset($original, $reencoded);
-            $failures[] = [
-                'path' => $path,
-                'reason' => 'byte_mismatch',
-                'original_length' => strlen($original),
-                'reencoded_length' => strlen($reencoded),
-                'length_delta' => strlen($reencoded) - strlen($original),
-                'first_mismatch_offset' => $firstMismatch,
-            ];
+            $originalJson = json_decode($presentation->serializeToJsonString(), true);
+            $roundTripJson = json_decode($roundTrip->serializeToJsonString(), true);
+
+            if ($originalJson !== $roundTripJson) {
+                $failures[] = [
+                    'path' => $path,
+                    'reason' => 'semantic_mismatch',
+                ];
+            }
         }
 
         $total = count($paths);
         $mismatchCount = count($failures);
         $testProIdentical = !in_array(self::TEST_PRO_PATH, array_column($failures, 'path'), true);
-        $message = "Binary round-trip results: {$identicalCount}/{$total} identical, {$mismatchCount} differ. Test.pro identical: "
+        $message = "Round-trip results: {$byteIdenticalCount}/{$total} byte-identical, {$mismatchCount} semantic/decode failures. Test.pro byte-identical: "
             . ($testProIdentical ? 'yes' : 'no') . '.';
 
         if ($mismatchCount > 0) {
@@ -94,22 +106,4 @@ class BinaryFidelityTest extends TestCase
         $this->assertSame([], $failures, $message);
     }
 
-    private function firstMismatchOffset(string $left, string $right): ?int
-    {
-        $leftLength = strlen($left);
-        $rightLength = strlen($right);
-        $limit = min($leftLength, $rightLength);
-
-        for ($index = 0; $index < $limit; $index++) {
-            if ($left[$index] !== $right[$index]) {
-                return $index;
-            }
-        }
-
-        if ($leftLength !== $rightLength) {
-            return $limit;
-        }
-
-        return null;
-    }
 }