diff --git a/components/content_settings/core/common/host_indexed_content_settings.cc b/components/content_settings/core/common/host_indexed_content_settings.cc
index 1f286ca1c49ea..04d7d4b259df9 100644
--- a/components/content_settings/core/common/host_indexed_content_settings.cc
+++ b/components/content_settings/core/common/host_indexed_content_settings.cc
@@ -13,6 +13,7 @@
 
 #include "base/check_op.h"
 #include "base/feature_list.h"
+#include "base/logging.h"
 #include "base/notreached.h"
 #include "base/time/clock.h"
 #include "base/time/default_clock.h"
@@ -299,17 +300,48 @@ const RuleEntry* HostIndexedContentSettings::Find(
   const RuleEntry* found = FindInHostToContentSettings(
       primary_url, secondary_url, primary_host_indexed_, primary_url.host(),
       clock_, return_expired_settings_);
-  if (found) {
-    return found;
+  if (!found) {
+    found = FindInHostToContentSettings(primary_url, secondary_url,
+                                        secondary_host_indexed_,
+                                        secondary_url.host(), clock_,
+                                        return_expired_settings_);
   }
-  found = FindInHostToContentSettings(
-      primary_url, secondary_url, secondary_host_indexed_, secondary_url.host(),
-      clock_, return_expired_settings_);
-  if (found) {
-    return found;
+  if (!found) {
+    found = FindContentSetting(primary_url, secondary_url, wildcard_settings_,
+                               clock_, return_expired_settings_);
+  }
+  // ---------------------------------------------------------------------------
+  // POC INSTRUMENTATION: re-adds the linear-scan equivalence check that was
+  // dropped after commit 1c1d85869069c. If the indexed lookup returns nullptr
+  // but a brute-force scan of the host buckets finds a matching rule, the
+  // index has diverged from the reference Matches() semantics and we abort.
+  // ---------------------------------------------------------------------------
+  if (!found) {
+    auto brute = [&](const HostToContentSettings& m) -> const RuleEntry* {
+      for (const auto& [host, rules] : m) {
+        const RuleEntry* r = FindContentSetting(
+            primary_url, secondary_url, rules, clock_, return_expired_settings_);
+        if (r) {
+          return r;
+        }
+      }
+      return nullptr;
+    };
+    const RuleEntry* lin = brute(primary_host_indexed_);
+    if (!lin) {
+      lin = brute(secondary_host_indexed_);
+    }
+    if (lin) {
+      LOG(FATAL)
+          << "POC: HostIndexedContentSettings::Find divergence — indexed "
+             "lookup returned nullptr but linear scan matched rule (primary="
+          << lin->first.primary_pattern.ToString()
+          << ", secondary=" << lin->first.secondary_pattern.ToString()
+          << ") for primary_url=" << primary_url.spec()
+          << " secondary_url=" << secondary_url.spec();
+    }
   }
-  return FindContentSetting(primary_url, secondary_url, wildcard_settings_,
-                            clock_, return_expired_settings_);
+  return found;
 }
 
 bool HostIndexedContentSettings::SetValue(