diff --git a/clang/lib/Analysis/UnsafeBufferUsage.cpp b/clang/lib/Analysis/UnsafeBufferUsage.cpp
--- a/clang/lib/Analysis/UnsafeBufferUsage.cpp
+++ b/clang/lib/Analysis/UnsafeBufferUsage.cpp
@@ -1512,8 +1512,8 @@
                         FixItHint::CreateInsertion(
                             (*EndOfOperand).getLocWithOffset(1), "[0]")}};
     }
+    break;
   }
-    [[fallthrough]];
   case Strategy::Kind::Iterator:
   case Strategy::Kind::Array:
   case Strategy::Kind::Vector:
@@ -1541,8 +1541,9 @@
       if (EndOfOperand)
         return FixItList{{FixItHint::CreateInsertion(
             *EndOfOperand, ".data()")}};
+      // FIXME: Points inside a macro expansion.
+      break;
     }
-      [[fallthrough]];
     case Strategy::Kind::Wontfix:
     case Strategy::Kind::Iterator:
     case Strategy::Kind::Array:
diff --git a/clang/test/SemaCXX/warn-unsafe-buffer-usage-test-unreachable.cpp b/clang/test/SemaCXX/warn-unsafe-buffer-usage-test-unreachable.cpp
new file mode 100644
--- /dev/null
+++ b/clang/test/SemaCXX/warn-unsafe-buffer-usage-test-unreachable.cpp
@@ -0,0 +1,8 @@
+// RUN: %clang_cc1 -std=c++20 -Wunsafe-buffer-usage -fsafe-buffer-usage-suggestions -verify %s
+
+// expected-no-diagnostics
+
+typedef unsigned __darwin_size_t;
+typedef __darwin_size_t size_t;
+ #define bzero(s, n) __builtin_bzero(s, n)
+void __nosan_bzero(void *dst, size_t sz) { bzero(dst, sz); }